My original thought was to match all the cones, for consistency of timbre. Perhaps that's not as big a factor for the effects channels, and I'm sure the crossovers are the same or similar (?). The specified differences between RS-42, 52 and 62 don't appear to be too dramatic, mostly power and low freq capability.
On the centers, why is "bigger = better" as opined here? Perhaps if room-filling-volume is important, which it is, but given the limited space I'm using I don't understand why 4 woofers will be better than 2 woofers when my ears will ultimately be only about 13' from the speaker.
One of the big draws for me with Klipsch is the effeciency of the speakers. I've helped others set up whole-house systems and casual listening areas and a positive feature is the flexibility in choosing amplification (lower power "needs", less expensive amps).
I like the concept of effectively using the RS-42, from an economic standpoint, about half the 62. The same goes for the RC's.