As spiffnme mentioned, either speaker will work wonderfully in your room. The two deciding factors for you should be
A) How loud you like your music
B) What kind of amp / receiver you have
The M80s play louder and cleaner than the M60s, but they sound the same when driven within their limits. Because the M80s are 4-Ohm speakers, you'll need equipment that can handle pushing a lot of current. This isn't really as big an issue as it used to be, though, since most modern receivers -- and even more separate amps -- can handle a 4-Ohm load.
