I have a 980ti G1, which is one of the most overclock-able cards out there. Many people push it over 1.5Ghz.
https://www.youtube.com/watch?v=uCGcZ4ilpNU
I run witcher 3 maxed out on my 1440p monitor and it runs really smooth. Smooth to the point that I cannot tell the difference on what is smoother still ;-) .
If 44.7 is average on a 980Ti you will get about 55-60FPS on the 980ti g1 and you can still OC it by another 25% where you will get to around 65-70FPS. SLI has lots of negatives which has to be considered before investing so much money into it. I rather reduce my Anti alias from 16x to something else and run the game at 100FPS because I have a higher than 60hz montor which makes a bigger difference.