Most of the reviews I have seen have the stock 8800GT slightly better than the 3870 but the OC versions of the 8800GT are the best as far as gaming goes. I think most cases these days extract the heat quite well.

If you are just looking at the stock 8800Gt I think I might go with the 3870, it's cheaper to replace down the road if you start gaming more or you could crossfire it as I think it is Crossfire capable now. Is that board crossfire capable?

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70