When i asked Axiom about powering my M60s, they recomended at least 100WPC, This being said most reciever manufacturers OVERATE the WPC. The exception to that rule is H/K which tends to underrate their WPC.
As far as 75WPC compared to 100WPC you are only going to get about 1-2 DBs more with 100WPC. Where more WPC comes into play is called "headroom". At any given point your reciever is only useing 1-5 WPC but at certain peaks in the music or soundtrack that number can jump up to 90-100 WPC (for a split second) and that is where you need more power to avoid clipping and distortion. IE "headroom'
This is how I uderstand that it works. If I'm wrong I'm sure someone will jump in and correct me.
