Honestly I feel that the Mark IV HBC, even with its cap of one, is borderline on the OP scale personally. Just as I feel that HBCs should remain galaxy capped, least they have to get hit with a really big nerf hammer, I can't see a Core Heavy Beam Cannon that isn't anything less than a Wraith Lance. A single focused beam that simply evaporates entire waves. You point it at a wormhole and nothing below MK III-IV Starships survives. And as much pure awesome as that sounds, it's in no way, shape, or form balanced. The Mark IV already hits really close to this, and is nearly too much.
PS: Keith, nerf my HBCs, ANY OF THEM, and there will be a mess.