I've added extra 80mm (quiet) Sunon fans to my Antec case and with my TaiSol cooler cooling my 1Ghz T-bird @1.1Ghz, my idle temps are low 20's with peak temps at high 30's (Seti, Prime95, RC5, 3DMark 2000 loops).
Cranking up the multiplyer to 12x100 (1.2Ghz) idle temps are mid 20's with peak temps at high 30's - going no higher than 41C under full stress.
The most important thing is that it runs 100% stable. If you can go to bed with 3DMark looping and wake up with it still running, you got a pretty stable system as far as the video card is concerned. If you can do the same with Prim95 running at the same time for at least 8 hours - things are looking pretty darn good for overall system stability.