PSU 750 minimum to get 4xPCi's.
Why can't you use a couple of splitters on CX600M or even CX500M. KnC is pushing ~400W through one PCIe cable. I am not suggesting to do it, though.
you can. the 12v single rail can do 456 watts. but if you don't own own don't buy it
look for this runs 3 s-1's and all wires are there plus a great sale with the rebate card under 160 usd