I just pieced together my new compy, putting me in as the leader in crunching times, tell me if i'm missing something here, but I think its true.
Specs:
K8N Neo Mobo
Athlon 64 3000+ D.O.T.'d to a current 3% increase ( I know, flame the newb)
Nvidia 6600GT o/c'd to 1.18 ghz memory, and 564 MHz core with stock cooling, case cooled with 5 fans in addition to the heatsinks, (cpu & gfx), and the extra fan on my psu.
Seti could use your GPU, but I doubt it does. More than likely you're creating noise on the AGP bus that's going to lower your memory access times/make it unreliable.