I have both the rpm and c4 both in the 2012 models
12m c4 and 9m and 7m rpms
jumping performance and kitelooping - c4 much better due to flying through the loop and reaching zenith to be caught. I find the rpm has a hard time getting to the top quickly which means a loss in jumping performance.
Upwind- C4 is better
Unhooking on the c4 is wonderful- passes are made much easier= more slack than rpm
For wave riding I like the rpm better due to its drifting capabilities
Low END- I would say rpm pulls harder per size than c4
When you fly an rpm you dont feel like you are riding a c kite but on the c4 it feels like a c kite, performs like one, and without the loss in depower and the hassle of 5 lines with true c kites.
Hope this helps