I would say if you plan on getting a new amp or receiver in the near future then get the m80's. If you think it will be some time before you can get a new amp then get the m60's.
I have m80's in a 2100 CF room (that is open to the kitchen and hallway) and they sound great.
I planned on getting the m60's since my room is fairly small and I wasn't planning on spending more than a few hundred on a receiver. However, I went to audition some speakers and the only thing I nearby was the m80's.... and after hearing the m80's I knew I would never be satisified if I purchased the m60's
I ended up buying a denon 3808 which I purchased from 6ave for $1100 (MSRP is $1599).
I am sure that the m60's are great speakers though (never heard them).
I would suggest checking in the "hearing things" forum and see if anyone is nearby that has the m60's or m80's. (or both) Maybe that will help answer your question.
