The only thing I can think that you don't need is a 850w power supply even if you were to sli 670s, 750w is enough and if you were to get a 680ftw a 600 or 650 would be enough.
How does the build look other than the too powerful PSU and the not too future proof GPU?
How much are you OCing?
As far as I can go while remaining cool. Not too sure on how high I can go because of the heat problems related to the new ivy bridge processors.