I somehow recall Ian saying once that the M80s have a longer bass extension and play louder than the M60s, but that was about it.
If you couple an M60 with a sub, which most ppl do anyway, i don't think you would be kicking yourself b/w that and the M80s choice.
But they are larger and may therefore have a macho, mine is bigger than yours kinda thing to them as well.

Just how big is your space?

"Those who preach the myths of audio are ignorant of truth."