I probably should clarify that, as I felt the Extreme III was limiting on the 50D too. When shooting raw bursts, the difference in speed clearing the buffer can be felt on the 50D comparing Extreme III and Extreme IV. The 7D has a bigger buffer which helps, but it still has to dump it onto card some time and clogs up all the same. If you use jpeg only then the card speed isn't so significant.
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.