In GPU land, 65c means you can just take off your sweater, in other words that is barely getting warm. The 8800GT you are looking will run just as hot, if not hotter. If you MUST get an 8800GT, but sure to get one that is dual slot that will exhaust air out of the case.
IMHO, if you are thinking of getting an 8800GT, get instead a 8800GTS 512meg G92 like I have. It will overclock 125mhz over stock and run perfectly fine, (and fast) and, they are dual slot cards with excellent cooling.
For my final 2 cents, I say just get the 4850.