What's to say? Stare at someone within 450 meters and hold down the triggers. 18 DPS is scary for anything on the other end of the barrels.
IMHO there is no need for armor on your arms: you can't torso twist when firing the RAC5, so you can't use them as shields. Also, IMHO you have too much ammo: with your fit (and pre-ammo skills) you can deal up to 1650 damage, around 1950 damage if we count both ammo skills, which is very unlikely. Also, remember that smurfy does not count the RAC in the heat efficiency, so you are going to be very hot without any additional DHS. This would be my attempt.
Running a single MRM 30, or MRM20+10 is more beneficial to that heat efficiency than 2 DHS, but overall I agree with Carlo here. Still, nice disruptive build!
That RAC on that high mount sounds nasty AF; may need to get myself one of these. While I don't think that the arm armor is necessary, I think it wound be nice to have; firing MRMs and then twisting tends to work well for me.