Yeah, this topic brings up a lot of issues, e.g. 'My SM commander has a power fist and lighting claw so he gets rerolls and S8 attacks at I4'
Simple rule: DO NOT ARM CHARACTERS WITH TWO SPECIAL WEAPONS.
It does NOT confer any cumulative bonus (you can only use one weapon or the other e.g. use EITHER the lightning claw or the power fist) and you don't even get +1 attack.
So don't try converting your units to be uber-2-special-weapon-people, because it doesn't help. The standard CCW/pistol thing is THERE FOR A REASON.
I can't stress it enough, just get one power weapon, and a pistol. It saves points you can use on other models, and you can use the spare power weapons to make other sergeants.