So I installed windows 8 this weekend. The windows system asses,ent tool maxed out at 7.9 in windows 7 and under windows 8 maxes out at 9.9. So I ran it and was a bit surprised when my graphics score only came back with a 7.1. I'm running two gtx 670's in sli. Really? Two 670's can't max out the old 7.9 vista score and can't even come close to the 9.9 in windows 8? What in the world would it take to get that 9.9? Two gtx 690's?
I get an 8.9 with my Crossfire 7970s, so you should probably get an 8.5 or 8.6 with SLI 670s. First thing I'd do is reinstall drivers.