Crossfiring 2 different cards

It's the first two digits that must be the same not the last two.

Those two cards are altogether from a different platform and thus cannot be put together.. IMO two cards should not be paired together unless they are basically the same as then the slower card holds back the faster card (like a 5850 + 5870 card setup, though will work, will mostly be like pairing two 5850's with the added expense for getting the 5870)..