It's all pretty academic if the speaker is truly 8 ohm (or even 6 ohm) - then you can just refer to power/spl tables (or calculations) and you are gold.Then again audible differences....
But then, heaps of full range speakers have impedance in the bass that drops to 3 ohm - and let me tell you from personal experience - when the AVR runs out of current - the soundstage ends up collapsing, sounding congested... it is an ugly thing!
Then you replace that amp with one like this Quad - not overly powerful into 3 ohm - but it does the job, remains stable, and provides enough power/current even at low impedances to do a reasonable job - suddenly the midrange cleans up.
Putting something capable of 1200W@ 2 ohm on the same speakers - clears up those kind of issues altogether! - but some would view that as excess...
And if you have full range speakers, it is worth checking, as it is always surprising how many of them have impedance that drops down low on the woofer...