It appears that one of the biggest advantages for Fury X over the previous generation is simply its improved tessellation capabilities.
Quote:
"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.
http://www.hardocp.com/article/2015/06/24/amd_radeon_r9_fury_x_video_card_review/11#.VZVIcJVRGUk