the F@H GPU client for nVidia cards does not support SLi or multi cards yet. So getting 2x280's wont get you to the top anytime fast. Since you will only be able to use 1 core of them all.
Not to mention that PVRT is almost at 1 Million there would be no way that you would beat him that fast.
That is what i do. I run the GPU client and the CPU client. That is how i was able to get over 20,000 points so far. Constantly running both helps. Even though my GPU folds 3x faster.
Well, after completing my big move across the counrty I finally had time to set up folding at home again. I installed the GPU client and am about to finish my first WU, so hopefully I'll back up the ranks in no time.