It seems that this bench is in Dx11, in Dx12 there should be a significant boost:
1920x1080
R9 290X DX11 = 45 fps
R9 290X DX12 = 74.8 fps
2560x1440
R9 290X DX11 = 32 fps
R9 290X DX12 = 52.5 fps
3440x1440
R9 290X DX11 = 25 fps
R9 290X DX12 = 41 fps
http://gameranx.com/updates/id/54685/article/total-war-warhammer-directx-12-benchmarks/
I wonder if the Dx12 will be available from the D1
EDIT - nvm, i've just found the answer!
We’re pleased to confirm that Total War: WARHAMMER will also be DX12 compatible, and our graphics team has been working in close concert with AMD’s engineers on the implementation. This will be patched in a little after the game launches, but we’re really happy with the DX12 performance we’re seeing so far, so watch this space!
http://wiki.totalwar.com/w/Optimisation_Blog