I'm running 2 Cards, on Windows 7 Ultimate 64bit and have a Silverstone Strider 1500w PSU
Do you use stock coolers? In auto mode or on 100% rpm?
I can't get, how do you keep temp at 68C.
My cards are separated with pci-e risers and heat up to 75-80C.
What software do you use for OC, MSI AfteBurner?
My 5850s are the sapphire xtreme ones, stock coolers running at 65-70% fan depending on the days temp, running at 100% will kill its life time
I'm using sapphire trixx for the OC, not sure why you are getting such high temps, maybe your OC software is automatically bumping the voltage.