I think the main issue with big speakers in a small room is making sure you have room to place them properly.
M60s are fairly deep and like to be 12-24" away from the back wall so figure the fronts of the speakers are going to be approximately 3 feet from the wall. As long as that doesn't pose a problem, they sound great in a smaller room although they LOOK pretty big from the side
If you are going to have the M60s on the short wall (ie playing "lengthwise") I would say "no problem at all". If you're looking at a projector setup I imagine that's your plan anyways.
If you're going to have the M60s on the long wall you're probably going to have to have the seating fairly close to the back wall -- just make sure that can be worked into your plans.
