Yeah efficiency and your room size and how loud you play.More likely to damage speaker by clipping an amp than running it with price greater than recommended rage though this has it's limits of course.But point about say lager "sound stage" isn't going to happen with same speakers and more power necessarily.But some speakers though like Maggie's,Sonus Faber's,B&W's etc can run on "X" but when you feed them copious amounts of power they come into their own.
Chazz
Chazz