There's a pretty good body of information for UC mobile suits at least. As we've discussed in this thread, mobile suit engagements tend to be resolved within a range of about 20 km, since they can't reliably detect each other beyond that. Based on MS Igloo and other sources, larger objects such as ships can be visually detected up to a range of 300 km at the start of the One Year War, which is further than the effective range of a Magellan-class battleship's main guns. By the end of the war, the visual observation range has been pushed up to more than 500 km, and one assumes it continues to increase; however, the 640 km cruising range of the Bawoo Nutter (which can function as an unmanned missile) is said to far surpass the effective range of beam weapons, so it appears that as of Gundam ZZ the range limit for beam weapons is still just a few hundred kilometers.
of the beams is a different, and rather interesting, question. Based on ZZ episode 34, the beam from the ZZ's high mega cannon seems to be about 30m wide; that may give us a reference point for other weapons.
Meanwhile! I mentioned that I was doing some further research on relative weapon power. Here's a selection of data that I've recently dredged up...
Its main gun is the large deflection type mega particle cannon that protrudes from the front of the torso, which is powerful enough to sink a Magellan-class battleship with one shot. Deflection type mega particle cannons for anti-air use are also arrayed around the torso to prevent mobile suits from engaging it in close combat. [...] However, operating all these high-output mega particle cannons requires the charging of a mega condenser based on Minovsky physics, and due to cooling problems full-scale combat can only be sustained for less than twenty minutes. (Entertainment Bible 1)
Transformable Mobile Armors:
In addition to transformation systems and movable frames, another technology developed in transformable MA was mega particle cannons connected directly to the generator. One Year War-era MA and warship main guns were also directly connected types, but the development of the mega condenser made it possible to drive high mega cannons with ten times the output of previous types. (This technology underwent further improvements, and was inherited by the mega bazooka launcher and 4th generation MS.) (Entertainment Bible 2)
The mega launcher is a weapon that was first introduced in the Gryps Conflict, and then underwent rapid advancement. Its range performance and destructive power are warship-class. (Entertainment Bible 2)
Mega Bazooka Launcher:
Due to improved mega condenser performance, it can be used by a single machine. However, continuous fire requires backup from an additional machine. (Entertainment Bible 2)
As you can see, the Entertainment Bibles spend some time discussing the "mega condenser," which is of course what makes the ZZ's high mega cannon possible. It's not entirely clear what makes these devices so "mega," but there's a more recent explanation in the Encyclopedia of Gundam...
Thanks to the improved performance of non-transformable MS, a 4th generation of high-class machines appeared which emphasized offensive strength. One result was the installation of high mega cannons. Beam cannons which did not use the energy CAP system, and could use energy directly from the generator (particle cannons directly connected via mega condensers), had ten times the previous output. This was implemented in the late 0080s as generator output rapidly increased, and it became possible to use mega condensers inside the MS itself to accumulate the electrical power produced by the generator and degenerate Minovsky particles.
It looks to me like, as a consequence of their higher capacity, these devices allow mobile suits - and mega launchers - to accumulate energy out of proportion to their generator output. The FAZZ, for example, has a generator output of just over 8,000 kW and a main weapon with an output of just under 80 MW, a tenfold ratio of generator to weapon output. It makes sense that these devices would also be used in mega launchers, which are huge weapons powered by one or two rinky-dink little mobile suit generators.
Even in its normal state, the long rifle mounted on the FXA-05D has a high level of destructive power. But when connected to MS power circuits with an external cable, it can also function as a mega beam launcher. (MG kit manual)
The term "mega beam launcher" is also used to describe the weapons used by the RX-78-4 Gundam, the Le Cygne, and the ReZEL. The Zeta's "hyper mega launcher" also used to be described as a mega beam launcher in the old kit manuals. It's not clear whether this category would be more or less powerful than the "mega launcher" used by the Mega-Rider, Hizack, Doven Wolf, and Jamru-Fin, but the latter two are rated at 40 MW and the Mega-Rider's main gun can be boosted to the level of the ZZ's high mega cannon using its supply of E-cartridges.
According to the HG-UC kit manual, the beam cannons in its fingers use the energy CAP system, while the diffuse mega particle cannons in its chest are connected directly to the generator. (Don't ask me why their output is so puny.)
According to the HG-UC kit manual, its mega particle cannons are connected directly to the generator. Entertainment Bible 2 estimates their output at 11.3 MW.
Another distinctive characteristic of the ZZ Gundam is its incredible firepower. In particular, it has a high mega cannon with an output of 50 MW. This high-output mega particle cannon gathers the electrical power of all the machine's generators, amplifies it with a newly developed mega condenser, and then fires it, and it has the power to sink a large warship. Its main gun and beam sabers also have performance far beyond those of traditional MS equipment. Its main gun, the double beam rifle, has mega bazooka launcher-class power and is also capable of continuous fire. The high mega cannon has 1/5 the output of a colony laser, the strongest of all weapons. However, because it concentrates the power of all the generators, the machine's functionality is temporarily decreased after use. (1/100 kit manual)
The MSZ-010's main weapon, the double beam rifle, has power rivaling that of a mega bazooka launcher but is also capable of continuous fire. This is because the module itself not only contains multiple generators, but can also receive an energy supply from the main body. (Master Grade kit manual)
Hyper beam saber / beam cannon: This can form a beam blade with several times the power and length of a normal beam saber. When mounted on the backpack, it can also be used as a beam cannon of a type connected directly to the generator. (HG/UC kit manual)
The high mega cannon installed in its head has power surpassing that of a warship's high-output beam cannon. (Gundam Collection)
Two interesting things here. The claim that the ZZ's high mega cannon can "sink a large warship" puts it perhaps a notch above the main guns of the Big-Zam and Doven Wolf, which are said to be capable of sinking a Magellan with one shot. Also, we're told that the backpack beam cannons are connected directly to the generator, which means they bypass the E-CAP system and use the generator output directly. So it's possible that their lower output in Core Base and G-Fortress form may reflect the fact that, without all the ZZ's generators connected together, these weapons run off E-CAPs instead and thus require a lower generator output.
Incidentally, the ZZ's "double beam rifle" is commonly listed as a "mega beam rifle" in Core Top and G-Fortress form. This term is also used for the rifle of the Nightingale, as well as the Mass Production Type Zeta and the Zeta II. Speaking of which...
Mega beam rifle: In waverider form, it can be structurally connected directly to all the generators, displaying power rivaling that of the Z Gundam's hyper mega launcher. (HG-UC kit manual)
In this case, the Zeta II's generators link together in waverider form, allowing its mega beam rifle to "power up". I suspect that the ZZ may work the other way round, linking its generators in mobile suit
form so that it can run all its weapons directly from the generator and concentrate all their output to fire the high mega cannon.
Its extensive armament is characteristic of the 4th generation, but the Doven Wolf also has a system in which its beam rifle can be connected directly to its fixed mega particle cannons and used as a mega launcher. The rifle's output is 12.5 MW, and the two chest mega particle cannons are 5.3 MW each. When they are used as a mega launcher, it has an output of 40.2 MW. Of course, due to its massive energy consumption and the need to recharge, it is incapable of continuous fire, but it has the power to sink a Magellan-class battleship with one shot. (Entertainment Bible 2)
Its most distinctive feature is the high mega cannon in its abdomen. With one blow, this weapon has the power to pierce the heavy armor of a warship from the very limit of its effective sensor radius, and sink it. (1/144 kit manual)
Notable chiefly for a couple of very specific claims about these weapons and their ability to sink warships with one shot. The Doven Wolf's 40 MW mega launcher can sink a Magellan; the Jamru-Fin's 30 MW high mega cannon can sink a warship of unspecified type. It's possible, then, that we may be able to rate weapons based on how big a ship they can annihilate!
Nu Gundam HWS:
It uses a hyper mega rifle, with power rivaling that of a hyper mega launcher, as its main weapon. (Gundam Collection)
Mega beam rifle: It can also fire super-high-output beams rivaling those of a mega bazooka launcher, and is equipped with a bipod designed for long-range precision bombardment. (RE/100 kit manual)
A couple more comparisons for our reference. The hyper mega rifle of the Nu Gundam HWS is comparable to a hyper mega launcher (presumably that of the Zeta), which puts it in the same ballpark as the Super Gundam's long rifle and the Zeta II's mega beam rifle. The Nightingale's mega beam rifle rivals a mega bazooka launcher, which would put it in the same range as the ZZ's high mega cannon and the Unicorn's beam magnum.