I think one of my 7950's is a bit weak

I can only reliably keep them all at 1050. These weren't the best cards just xfx "double d" base models. They are located in a basement that's around 60f and not in a case still hitting 75c on the top card then a couple degrees lower for the cards.
I have a couple of XFX 7950DD rev3, one will do 1100MHz with no monitor and the other 1025MHz @ 1.030V (default), but monitor drops that by about 70MHz, the rev5 I have will do 1200MHz all day long @1.250V (default) but drinks the juice, mostly run them @ 700MHz where the voltage drops to 0.95, the rev5 (asic 66%) system, 2 cards pulls 250W, the rev3's (asic 87%) x2 pull 330W at 700Mhz.