I haven't read or played Halo but the snippets I'm seeing here of the technology shows high levels of bogon flux. Part of the purpose of an electromagnetic cannon/rail gun is that you can put cheap metallic slugs in it. Having all that expensive coils and switching but only a couple tuna cans for it sounds like poor planning. And read Mike Wong on plasma weapons. Not the greatest choice for beam weapons combat, if you accept his arguments.

For a good match to the Federation you don't have to look far (Constitution-class against White Star, anyone?) The Empire takes a little more shopping around. I'd look to "Doc" Smith for forces that are properly galactic, plus have the proper fire-power. The Weberverse might be able to throw numbers at a single fleet engagement but they'd lose the war.

One I'd like to see is Empire invasion force v. the "Federation" of James H. Schmitz. No organized, monolithic force ever showing itself. But "Tuvela effect" on every durn world Imperial troops took on. It would probably end in victory for the Empire -- but they'd have a lot of grey hairs.