in evaluating amps for 4ohm speakers like the m80, do i look at amp's 4ohm power rating instead of its 8ohm power rating? conversely, do i look at the same amp's 8ohm power rating when matching it with 8 ohm speakers like the m60?

for instance, a stereo amp is rated 250w/550w in 8/4 ohms per channel, respectively. for the m80 (max amp power of 400w at 4ohms), can i say that the amp is more than sufficient to drive the m80's since the amp rated at 550w in 4ohms? for the m60 (max amp power of 250w at 8ohms), do is say that the same amp is just enough?

in relative terms, however, does it mean i have more reserve power using the same amp with m80's than the m60's (550w/400w at 4ohms against 250w/250w at 8ohms).

please enlighten. thanks.