You could run either setup, but you'd have more OC headroom with the 670s.
totally wrong but OCed is HD7970 can do alot better
just so u know i have myself a GTX670 and it runs amazing dont get me wrong but the whole turbo boost thing is weird and depends on you get used to it and temperature, also catalyst 12.7 will give 7970 even more headroom
all i can get on my GTX670 is 1215 core and 1700 memory
You didn't take my reply in context. He was asking about which setup to go with his PSU; the 7970s could run on it but he would not have the OC headroom that he would with the 670s. That is to say that 670s could be overclocked as far as they will go on air with that PSU without running into a problem, whereas with the 7970s there is the distinct possibility of maxing out the 12v rail with a heavy overclock of 7970s in CF. Of course the 7970s are better overclockers, that was really my point.