I have two twin frozr II 6950s and a refrence msi 6950(unlocked shaders) setup in xfire in win7 64bit. My first problem is the middle card (frozr) is overheating even with 100% fan speed it gets into the 90s. I haven't even bothered with overclocking yet but in CCC I set powertune to -20% on this card and it still gets into the upper 80s but its performance goes down a lot. My system still crashes too! I have a 1.2kw power supply so power shouldn't be an issue. Do I have to go water cooling just to get my temps under control for 3 cards?? I'm considering it anyways as I'd like to have 3 cards pushing 400+ mh/s each
Get a second (smaller) power supply, put one or two of the cards on that. As for thermals, I replaced the chincy fan on mine with an intel heatsink fan. Roars like a jet engine but keeps it below 80. As a warning, you will have to mould plastic and it will violate your warranty to do this.