In terms of performance there wasn't any game where the AMD Radeon R9 Fury X was faster than the GeForce GTX 980 Ti. In some games, it did match the same gameplay experience, which was a major upgrade from the AMD Radeon R9 290X. However, in every game the GTX 980 Ti always had the framerate advantage, especially when it came to minimum framerate which is important.
At 4K, where the AMD Radeon Fury X is supposed to shine, it was still mostly beat by the GeForce GTX 980 Ti in performance. Only one game in our lineup was a bit faster, and by "a bit" we mean 2.4 FPS average than the GTX 980 Ti.
On the other hand, the AMD Radeon R9 Fury X was a major upgrade from the AMD Radeon R9 290X. We saw at times very large performance increases over the R9 290X, depending on the game.
The problem was though that the performance increases were very erratic. There wasn't a predictable percentage of performance increase with the R9 Fury X over the R9 290X. This is because the R9 Fury X is faster in some cases where games use heavy tessellation, since tessellation got a big upgrade in R9 Fury X. However, if a game doesn't use some feature that was beefed up in the R9 Fury X the performance increase over R9 290X is much smaller.
This means the kind of performance upgrade you will get over AMD Radeon R9 290X will depend on the game and the features it uses. Games like Witcher 3 and FC4 can bring big improvements. Older game like BF4 not so much. This means older games may not see as large improvements as newer games using newer technologies.