The M60's sound very similar to the M80's, the M80's will play louder, and to me they sound for a lack of better words a bit fuller, but that may well be because of my acoustics and room size.
I think you would be more than happy with the M60's, the main reason I upgraded was that the room the M80's are in is about 50'x 20' with 11' vaulted ceilings and I wanted a lttle extra power.

A computer once beat me at chess, but it was no match for me at kick boxing.