Yeah, I think this is one 'Mech I'd want to avoid the ghost-heat often, which means running a pair of 40s instead of 30s may not even be worth the added alpha, since it could mean so much longer exposure time. Should be able to put out a solid 3-400 damage before overheating though, on an average match. And that's really not too bad.
The ghost heat penalty on 2xMRM40 is negligible. It's a question of 23 heat for chain firing them, or 24.61 heat for the 80 point alpha. That said, when I'm running QP with my IV-4, it's always with 2xMRM30. I save the extra tonnage so I can bring more ammo. I only use the 2xMRM40 build in Solaris.
Instead of 2xMRM30 I would really recommend MRM40+MRM20: MRM40 has the most Damage per Heat, and the DPH for MRM20 is better than MRM30, too. With this I could start with alpha strikes or chain fire until running hot, then switch to only MRM40. See my IV-4tyTwenty build: https://www.mechspecs.com/threads/iv-four-iv-4tytwenty-mrm40-mrm20-2xml-jj-le270-std255.13435/ I just used it today and while I did not break 1000+ I got: 961 damage, 5 kills, 3 KMDD, 13 components destroyed (we lost 9:12)
