MRM50 has the best balance for speed, firepower and heat management for 55 tonners. Speed is life, don't go lower than a 280.
https://mech.nav-alp...bee2c9ee_GRF-1N
https://mech.nav-alp...18892f98_GRF-1N
Also, never take a MRM40+20 on any mech. The weight savings is not worth it because
1) you can't alpha without ghost heat, lowering your DPS. and if you chain fire, you increase exposure time. coupled with your slow speed, which means even more exposure
2) the MRM40 launcher has a different cooldown time compared to other launchers, so your weapon fire don't sync up even if you eat the ghost heat to alpha strike
Always MRM30+30 on mechs that can carry it. the 1 ton weight savings is never worth it.
This comes from testing all the various combinations through hundreds of matches in both my WVR and IV-four MRM brawlers