I think there are two issues here 1. Dual Channel ram and 2. Running the cpu and ram in sync.
Dual channel offers only a small increase in performance on AMD ysytems (bigger increase for intel cpu's running in dual channel). Running the ram and cpu at different FSB speeds hinders performance in AMD systems. If you're thinking of getting, say a Barton cpu it's FSB is 166. Then you're going to want ram that's at least pc2700 (FSB at 166), better still is pc3200 (FSB at 200).
If you get pc3200 and good mobo (e.g., Abit nf7-S) you can increase the FSB of the Barton cpu to 200. The ram and the cpu are in sync (this also is sort of an overclock for the cpu).
So if you get a faster cpu, you should get the faster ram. The dual channel thingy is relatively unimportant.
Hope this helps.
MSI KT3 ULTRA-2 KT333
Maxtor 60GB ATA 133 7200RPM
ABIT G4 Ti4200 OTES 64MB