Damn, too bad you didn't push for another 20$ and get the Pro version; you'd be able to do 8x/8x. 4x will slow down a 6970, by too much IMO that I wouldn't buy another card of that price.
The PSU sounds fine though.
EDIT: unless I'm reading this wrong and your bonus is for the WHOLE rig and not just the card! If you're buying a while rig, then upgrade the motherboard; 4x in SLI/CFX is NOT good! Either upgrade for a p8p67 Pro or get an Z68 based board (if you don't care about SRT or QuickSync, then you could save a few bucks in staying with a P67 based board)