Lawsab,
I was going through the exact situation about 2 months ago on deciding which speakers to get. At first I was set on getting the M22's since they were cheaper than the floorstanders. After speaking to some Axiom members, I found that while the M22s are excellent speakers, they cant really be compared with floorstanders. I thought what the hell (and since I always suffer from could of, would of, should of) decided to get the M60s.
Like others have said, it all depends on your budget and how much you want to spend. If you have the ends then go for the highest you can afford. One thing I really like about Axiom is that it costs very little to jump to their higher-end products.
I think (and its just MY lay opinion) the jump from the VP100->VP150 and QS4->QS8 are mostly for the larger sized rooms. They *might* sound similar in smaller to mid sized rooms but again I'm no expert. The jump from QS4 to 8s is only $100 so I figured what the hell, get the best one. Same mentality for the center, difference is $145 so I went ahead and got the VP150. Also, factor in the additional cost for the M22 stands and you're close to the price range of floorstanders.
You really can't go wrong with any selection you decide, but I'd say invest in the best your budget allows.
