The graph seems fake (an estimation at best). The markers for 1 gtx 690 and 1, 2 titans are equally divided among the bars. Although I do not have a 690 in my possession, the 690s (99% sure) and the titans (95% sure) that they do not scale 100% and vary title to title, which is what those markers indicate. Here are some BF3 benchmarks showing 1, 2, and 3 gtx 680s in sli:
http://www.guru3d.com/articles_pages/geforce_gtx_680_3_way_sli_review,14.html
at 1920x1200 you see a 77% increase from 1 to 2 (roughly a 690) and a 4% increase from 2 to 3 680s. I can't imagine adding a fourth (~2 690s) would add any more significant fps.
I would have loved to see a comparison to 2 7970's in CF mode and a 7990. Perhaps in the near future Tom's?