Will a Sapphire 7850 OC ( PCI-E 2.0 ) work on an Asus P5K Deluxe Mobo

There's no reason for it not to work. PCI-E 2.0/3.0 cards have backwards compatibility. I'd just check to see if the power supply can run it or not. A HD7850 will give you better performance over the HD6850 at around the same power consumption but the price difference is greater.

Don't worry about the power consumption - both cards will draw less than the 8800GTX but I'd seriously suggest an upgrade to the motherboard/cpu. It may be pointless as the performance of the gpu will be limited. Can you post the rest of your system specs?

Hi there, thanks for responding.

I agree with you that I need to upgrade my mobo/cpu however I wanted to do it a little later on as my system even though oldish, worked pretty good. However my 8800 GTX started raising temperatures over a 100 degrees so games were starting to crash.

So I need a better card but I can't get a really high end one. Power consumption is not really a problem for me, but performance / price.

Thnx   Changed size.

@OP, Maybe this article is what you looking for:
http://www.tomshardware.com/reviews/gaming-graphics-car...