Looks like SLI scaling is genuinely bad, at least on Metro game.
Maingear Shift Microsoft Windows 8.1; 4.5GHz Intel Core i7-5690X (OC); 16GB DDR4 SDRAM 2666MHz; (3) 4GB Nvidia GeForce GTX 980; (2) 250GB SSD RAID 0 + 1TB 7200rpm HDD - very powerful CPU with ultra fast RAM, and dual GTX 980 - 90 FPS according to the results.
Velocity Micro Raptor Z755 Microsoft Windows 10 Home; 4.0GHz Intel Core i7-6700K; 16GB DDR4 SDRAM 2400MHz; 4GB Nvidia GeForce GTX 980; 400GB SSD + 2TB 7200rpm HDD
Also very fast RAM, and CPU and Single GTX 980. 69 FPS. Only 21 less than from dual GTX setup. I would love to see comparisons between old and new technology directly on that type of computers. Otherwise we cannot give any proper judgment on that.