just set up a crossfire on my rig with a 6850 and a 6870

havent tested it, but I can't wait.
the only issue you should have is the board itself that I Can think of. I have an i7 and crossfire (just set it up right before posting this) and so far no issues. you need to make sure your board supports CrossfireX though as Intel and SLI go hand in hand unless the board has the technology to handle CrossfireX or SLI irregardless of Intel/AMD processor.