I really like the phrase "hear my money". Good one.
I won't dispute those folks who say they hear a difference between the two; I've heard both, but not in the same room.
And I think there is an important clarification missing from the discussion. It's not "can you tell the difference between the M60 and the M80 when only those speakers are compared?" - it seems to me that - for most people - the more relevant question is "is there a commensurate qualitative improvement in 5.1/7.1 listening when spending more to get the M80's than the M60's?"
Again, I don't KNOW "the answer". However, I would submit that the differences between the two are far more noticeable when you're NOT using center and surround speakers and when you're NOT using a sub.
Since I can't remember the last time I listened to either music or video content in 2.0, and my M60's play as loud as I want them to, I don't really have any heartburn. For me, I'd rather spend the money on other system improvements that I think make more of a difference (bigger TV, better sub, rear speakers, BFD, upgraded finish, etc.). YMMV.
We are a whole community of "that guy" - StPatGuy