PSU 750 minimum to get 4xPCi's.
Why can't you use a couple of splitters on CX600M or even CX500M (maybe too close for comfort). KnC is pushing ~400W through one PCIe cable, but they are cooling the plastic connector through a hole/fan. I am not suggesting to do it, though.
You gotta be real carefull with splitters, I have melted 2 plugs so far and they were only pulling 400 watts through them