I just upgraded my graphics card to a Sapphire HD 5850 and boy does this sucker overclock like mad!! Wow..
This is what im getting in the pic below and its VERY stable and VERY reasonable temps for idle (38c) and load (56c max) when i give it a good hardcore beating for a few hours playing crysis at a time.. never went above 56-57c.
Im getting around 60fps in Crysis in dx10 with AA x2 and AF x16 and all settings extra high in Crysis. It does dip to around 50fps once in a great while but over all its pretty steady in the high 50s/lower 60s. Im aware Crysis is more gpu dependent then cpu dependent but regardless.. im sure my Intel Quad Core QX9650 @ 4.6ghz helps a bit with the stable frames.
EDIT: Forgot to mention.. its amazing how much a good quality case helps with air flow though.. i just picked up a Antec Three Hundred case.. i had the card in my old case at first.. a smaller case and not nearly as much air flow.. my antec three hundred has three 120mm fans and 3 other case fans as well and i adjust the air flow of the fans to sweep out the hot air towards the back end of the case.. on my old case..the card was around 7c hotter all around.. 7c's cooler because of a case upgrade is quite satisfying to me. 60 bucks at the egg
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129042