I've just ordered 2x ASUS GTX 670 Direct CU II 'Non TOP' cards for SLI use in my 2600K system. My current MSI GTX 670 reference will go in my secondary system (Connected to a 1080p LCD TV in my living room), based on a Q9650 overclocked to 4GHz and DDR2 mem.
So will report back if I see bottlenecking, which I'm sure there will be. Q9650@4GHz even bottlenecked my previous Gigabyte GTX 570, a little bit. It varies greatly between games and resolution though.