I think the general feeling around here is that the M3s are good speakers to have if you don't have a sub, given the choice between M2s and M3s. The M3s have a slight hump in the bass (someone else, I'm sure, will provide the graphs), while the M2s are pretty flat, similar to the M22s and the M60s. Given that you don't have a sub at the moment, I'd say you're doing fine. As to room size, I'm not certain, but given your restriction on visibility, you're stuck with bookshelves (not that that's necessarily a bad thing...)
In short, give 'em a shot, see what you think, and send 'em back if you don't like it. In the long run, it's what you think that matters.
However, I'm getting the M22s. They're remarkably small in person.
Confused yet?
