Personally, I would go with a 5.1 setup right now for two reasons. It will allow you to upgrade to M60s and QS8s which have better depth, midrange and power than the M50s and QS4s and 7.1 in your present room imho doesn't seem necessary. You could add your rears if and when you set up a larger theatre where the M60s would be a better choice in the future room you described. I don't know what your budget is but my own preference, (re. MY) would be to go this route and add rears later if you go to a larger room but not compromise on the 5.1. In the end, it's what YOU want though, happy speaker hunting!
