Clan ERPPCs and Heavy Large Lasers hit fairly hard(15 and 16 damage respectively). I'd probably give them Improved Heavies, if they're an energy-focused group. But if you want something else up in the AC/20 or Heavy Gauss range, maybe something like these:
ER XL Laser - 20 damage, 10/20/30 range, 35 heat, 10 tons, 6 slots
XL Pulse Laser - 20 damage, 8/16/24 range, 30 heat, 14 tons, 8 slots, -2 to hit
ER Heavy PPC - 25 damage, 7/14/23 range, 25 heat, 12 tons, 5 slots
They're getting into the realm where they're hard to use on practical mech designs, but for WarShip anti-fighter defences or for ground-based fortifications they'll be monstrous, and occasional specialized designs could roll out with them as well. (Note that these were balanced by gut, not by math, so I make no promises that they're fair. And of course, a faction that has this kind of kit should also have drawbacks somewhere else - maybe no advanced missiles and no Gauss tech?)
