Err ... no? The x[number] is just the amount of lanes the PCIE slot has. Most cards, even if they aren't made for multi-GPU setups use x16. And x32 doesn't exist yet, afaik.
Damned Aussies ...
6850 w/ the modded bios to fully unlock it is probably a better choice in terms of price/performance. Or even the 6770 if he doesn't need anything really fancy