I have M60s and a VP100. Very happy with both. People seem to find VP150 is better when the room is big enough that you are sitting a fair distance from the center channel, maybe 9-10 feet being the point where you should start thinking about VP150 (this is very approximate).
Between M50 and M60 that is tougher... the M50 seems to be a bit more recessed in the midrange so will probably sound better in a "bright" room, while the M60 is flat enough that it will sound extraordinarily good in a room with a good mix of reflective and absorbent surfaces but might sound a bit bright in a room that is all reflective. My feeling was "go with the M60 and fix the room" but most speaker mfgs seem to dull down the midrange to suit the typical unprepped room.
Are you sitting facing the 10 foot wall or the 16 foot wall ? If facing the 16 foot wall then the M60s and VP100 are a no-brainer choice... if you are facing the 10 foot wall and sitting way back from the speakers then you might want to think about VP150. I think you would be happy with M50 or M60 in that room... and if you are facing the 16 foot wall (ie not sitting too far from the mains) then IMO M22s would be fine as well.
If you are going to listen to a lot of music and prefer jazz, acoustic etc... then go with the 60s or 22s. If mostly rock or your room is fairly bright then I would go with the 50s.
Don't read too much into all of this. I A/B'ed M3s and M60s and was surprised how small the difference was between them... and they are about as different as any two Axiom speakers you can buy
