According to the articles out today, with the latest drivers at the time the articles were started:
1) For single cards, the 7970 is superior.
2) In SLI/CF without FPS limiting or v-sync, 670 SLI is better
3) in SLI/CF with FPS limiting or v-sync, the CF problems disappear, I have not seen speed comparisons except for 1 game, which looked the same. Though FPS limiting favors SLI since you don't need to FPS limit SLI.
http://www.pcper.com/reviews/Graphics-Cards/Frame-Rating-Dissected-Full-Details-Capture-based-Graphics-Performance-Tes-10
http://www.tomshardware.com/reviews/graphics-card-benchmarking-frame-rate,3466.html
I have fun 6950 CF and 680 SLI, and I ran with v-sync most the time with the 6950's, before I knew about the latency issue that cause me simulator sickness. Now I'd play without v-sync more often.