Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.
I am sure there was some motherboards going to be released which had some chip on it that meant you can xfire/sli two different cards. Can't remember the name of them now, sure someone here will know.
I have a 5850 I could CF it with the 5870 then?.

Yes.
Crossfire doesn't downclock either (Another thing which people keep getting wrong).
The cards will run their respective clocks.
yeah but it's not reccomended , there are a few driver problems