the uk hw review I lined has 2/3/4 way 980 sli benches.http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_970_SLI/20.html
That is 970 SLI, I imagine 980 SLI is better.
It would be nice to see a benchmark with the GTX 980 SLI and a R9 290X in crossfire or a R9 295X.
This.$1,100 980 SLI is only 18% faster than $660 970 SLI at 4K. I would either get 2x 970s and pocket the difference towards GM210s or Pascal or get 3 of them. With 4K you want the most graphics horsepower so $1,100 for dual 980s is inferior to 3 970s, while 18% more performance for nearly double the price is absurd.