I have 5 cards running on win7 x64 as well with no problems. My guess is the 6950 with unlocked shaders is crashing. I have 2 6950s that worked fine with unlocked shaders until I used them for mining, then they would crash after a few hours. I had to switch back to stock bios to keep them working while mining. Try running just your 6950 solo and see if your system still crashes. If not just go through your cards solo mining 1 by 1 until you find the one that's unstable

Nofee has never worked for me either. I can connect to them but all I get is rpc errors so I dropped them altogether. I think there is an updated cfg file for btcserv a few pages back that should work, but I still get a lot of connection problems with them too