I was in the exact same position as you. You might have read my one of my posts aleady. Smallish condo, 800sq ft and wanted something that would fit in without being too bulky and taking up the valuable space. I know what it's like to constantly rethink things. I went back and forth from M22's to M50's constantly for about 3weeks and had the exact same questions you did. I even included a rough layout of my home. I can honestly say I had an easier time buying my condo then deciding on the speakers. In the end I placed my order on Monday for the M50's and the 150 Centre, and an HSU STF 3 sub. Rears are coming later.
My reasoning was I had a choice of two tv stands that I liked for the price. Both oddly enough from Costco. One was 80" long and the other was 60" long. I have a 42" LCD. I figured that if I got the 80inch stand I could put the m22's on the stand on each side of the tv or get the smaller stand and put the towers basically taking up the same space more or less. My other reason was that I thought floor standing speakers in HG Cherry (free upgrade) made for a sexyclassycool look as well as puts upgradeitis away for a long time. From everything I read here, it appears either way you can't really make a mistake. In the end I just went with my gut feeling as to what I really wanted in my heart. I think when it comes to space the sub for me is the hardest item to place in a condo. It would be nice if you could get a really good quality sub that fits under a coffee table
M22's v3, 2 x EP500v3, VP150v3, QS4's, Denon 3808CI
My Botswana Safari photos http://smu.gs/R41Byt