For that room size, the VP100 should be fine. If any of the following are true, you might want to go with VP150 :
1. You are sitting as far back from the speakers as the room allows, ie speakers are on one wall and sofa is against the other wall. There are no hard and fast numbers but if you are approaching 10-12' away from the center channel then I would go VP150.
2. You like to play really loud and the M22s are only barely keeping up with your SPL requirements.
3. You expect to move into a larger room with larger mains at some point in the next few years.
4. You have a tendency to come down with upgradeitis and long for the next model up even though what you have is working perfectly fine
