To clarify a bit further, you have to choose what weapon you use each combat not round of combat (i.e. you are charged by Unit X and opt to use the power fist. You must continue using this fist untill you are no longer in combat before being able to use the sword.)You gain the attack, but as you say, you have to choose which weapon you're actually using in each round of combat. You can't divide attacks between them.
IIRC that is not true Thomo, you are allowed to choose which weapon you want to fight with in each round of combat. So if your commander charges or is charged, he can fight with the power weapon or powerfist (having to choose one or the other before anything more is done), and next turn, if that enemy is not wiped out he may switch over to the other weapon if you so want him to.You must continue using this fist untill you are no longer in combat before being able to use the sword.)
Short answer.. YES..Hehe, humour aside, does the Living Metal rule also negate powerfist bonuses? Cause if it does then we've been doing something majorly wrong ;o