I have the m60s in a 15x16 room that is partially open to the kitchen. I love the sound out of my speakers. For music the m60s bass response seems perfect. Initially when i bought them I was disappointed with the bass. Before I got them I used to have my sub gain turned way too high. Now that I have everything dialed in and the sub and m60s are matched, i can turn off the sub and not miss any of the beautiful sound. In fact, without the SVS PB-12 sub, the bass is tighter and slightly more satisfying for music. However, for rap and other low frequency bass heavy music, the extra low frequency punch from the sub really helps.
For home theater a sub is required. The speakers reproduce most musical bass, but the floor shaking rumble is not there for movies. Without the sub you miss out on a lot of the LFE on well produced movies. The m60s can shake the couch a little bit, but fall off quickly on the low bass that puts the punch in movies.
The mids on the m60 are wonderful. Very clear. They are head and shoulders better than my old B&W 602s.
The highs are clear and detailed. I personally love the sound but I can see where some people would think they are bright. At really high volumes they can strain my ears slightly and I would not want to listen for ages at that volume, but at normal volumes, they are great. I don't have a treated room. I have hardwood floors with a rub covering 50% of the floor, a couch, ottoman, leather chair, and the back wall is actually a sliding glass door with a curtain over it. The curtain probably absorbs quite a bit of the sound, keeping it from getting over bright.
I would get the m60s over the m50s anyday. However, if I did it again, I might consider the m22s. Paired with my sub, they would sound great and I would have saved a little money. For HT the m22s and a really powerful sub would be great, but I think I would still get the m60s anyway.