Just wanted to throw in my $.02 of agreement with the majority of the posters above: I recently took the first step along the exact same upgrade path, having had 4 mini monitors all around with the CC370 on center duty. If you are really into running 2 ch stereo without your sub on, then I could see going with the Monitors, but given your svs, I think you'll be happier in the long run with the Studios. Upon listening to the two back to back on the same equipment with some Miles Davis, Norah Jones, and Pink Floyd, I guess my reaction was similar to warpdrive's, with the 20's coming out as the more "sophisticated" sounding speaker (smoother, cleaner, and in particular I was sold by the fantastic imaging and ability to disappear). Granted, the Monitor's are no slouch, but I think the Studio's are just that much better. And looking ahead, I'm more than a little excited about upgrading my center to the 470 or 570 once my wallet has recovered, (and upgrading to 40's or mabye 60's, etc. etc., we all know how the bug works....)
Just go and give them both a good audition, and my money is on you walking out the door with the 20's in hand!!