How much of a difference does a good GPU make in these tests? My ruffus cascade should be done in a few weeks, and I know I can get 5.2GHz benching stable out of this 920. However I am rocking a 8800GTS 640, and don't really see me upgrading for a while.

Although I could throw the 8800GTS under a single stage and throw a whole lot of voltage at it. However even then I think it is a lil' outdated.