anything colder than the air/water at ambient temps helps.
I have modded and benched a few 8800gt's, and each of them acted differently. Some jumped .05, others jumped almost .1, and one barely jumped at all. The one that didn't bump up under load clocked the worst, and was sold promptly. A .1 jump shouldn't hurt you too bad until it switches back to 2d idle... that can really throw shit into unstable land. Use Riva to lock the card into 3d perf. mode.