Congrats mkenyon...the GTX 690 is looking tight! If I could find two of 'em I'd simplify my setup. Not going to work too hard on it, though.
I don't recommend anyone to go quad-SLI right now. Drivers just aren't there. Lots of funkiness.
Can you elaborate? Sometimes in SC2 (tri-SLI), the game won't load my textures, or one of the cores clocks down to like 300 mhz. Reinitializing the driver or resetting the overclock seems to fix this. Are you experiencing anything similar?