Seems to me you have a lot of facts, that's good, to each it's own. What speakers are you using.??
I am using MB Quart QLS 830.
4ohm
87dB
I was running them off of a Yamaha rx-v1400 rated 110w @ 8ohm. Not 4ohm stable, and not rated for 4ohm use. I used it to run my system for about a year without any problems.
With a concern of clipping my receivers amp, due to the 4ohm load, low sensitivity, and large room size, I added an external amp.
Amp is an Adcom 7605, rated 175w @ 4ohm. No audible difference.
+1 Reduced the load on my receiver.
+2 Reduced the chance of clipping. Amp also has clipping indicators, which is nice.
EDIT: I added the amp for reasons listed above, not for an audible difference.