I just got the Lord Zhufor the Khorne terminator lord model and he has a power fist and power weapon. I am converting him into a night lord terminator and would have just replaced his power weapon arm with one with a storm bolter but the storm bolter is attached to his powerfist. I already have two models with power weapons and storm bolters in the squad. So if I have to choose one I will go with the fist just so have one in the squad.
I now just have to figure out what right hand I will replace the power weapon arm with.