I'd heard the same about 5.1 vs 7.1 but a short while ago had a chance to sit down and listen to a friend of mines 7.1 setup using the Onkyo TX-NR709 (which is why I chose to go with the 719). For some reason I noticed quite a bit of difference in some of my favorite movies going to 7.1
I think it's mostly the source material I was using, being the heavily special effects type movies we watch.