You don't even need 1 980ti for max settings on 1080p these days, it should be a very long time before you would ever need to replace those to run games at 1080p.
You don't even need 1 980ti for max settings on 1080p these days, it should be a very long time before you would ever need to replace those to run games at 1080p.
Seeing as one is currently plenty for 1080p 144Hz two of them is major overkill today so should last a long time. 3 years of max settings seems a good guess, possibly longer
1) It's impossible to tell the future. You should be good for a while but exactly how long is anybody's guess.
2) A single 980ti is plenty for 1080p @ ~120 Hz (FPS) with a good i5 or i7
3 years is a pretty good minimum. Considering that you really only need a 970 or equivalent for maxed-out 1080p (http://www.tomshardware.com/reviews/best-gpus,4380.html), & the 970 is usually able to get decent FPS even at 1440p (http://www.techspot.com/review/1174-nvidia-geforce-gtx-1080/), I would say that a single 980Ti is going to last you a long time, let alone SLI'd.
with that setup you will have closer to 5+ years of worry free gaming at max settings.
That is however if you stick with the 1080p res.
If you sometime in future plan to get a higher resolution screen then i would have to agree with most people here stating 3-4 years time.