I agree with everyone else here that if you overdrive a lower powered amp, you can blow the tweeters even in robust speakers. I like Blackraven's idea of trying to get an amp that has good behavior (e.g. soft clipping) when overdriven.
NAD makes a "soft clip" amp I think.

Reserve head room is a game that's played on the reciever market for sure and the danger of roasting you're speakers is real if you turn it up too long on lesser models. The HTR series ( I think it's HTR ) from Yamaha and the RX-V line definately do not have the same power supplies in them and the specs are deceptive. For the HTR series they pick a narrow band of frequency(s) that's easy drive and rate the amp at - let's say at 100 watts a channel. That's not the same as 20-20 at 100 watts a channel.