Recently Computerbase performed a few tests at 3840×2160 (Ultra HD) with HDR enabled games. The results are quite surprising, as they show NVIDIA graphics cards performing worse than AMD hardware in the latest games.
This deficit in frame-rates is more glaring at 4K, and although it does not make playable games unplayable, it does have an impact of roughly 10-15%. To top it off, AMD Radeon Vega cards are showing little to no deficit.
Assassins’ Creed Origins sees the most losses in performance with a drop of almost 6 frames, while the Radeon Vega 64 has no apparent drops. This pushes the GeForce GTX 1080 below the Vega GPU in this as well as other tests. The FPS drop is less noticeable in Far Cry 5, but both Final Fantasy XV and Battlefield 1 show visible drops.
NVIDIA at a recent presentation refuted these claims, but it does seem to be happening at atleast 4K at the moment. 3DGuru conducted some tests of their own, and noticed little to no difference for NVIDIA GPUs at 2560×1440. Maybe NVIDIA fixed it in a driver hotfix.
The site further explains that this performance deficit is possibly due to the way NVIDIA converts RGB to reduced chroma YCbCr 4:2:2 in HDR. In ComputerBase’s testing, they used a similar testing environment. If they used 4:4:4 or RGB, the performance would have been the same as SDR. GSYNC when used in 4Kmonitors scales down to 4:2:2 which is most probably the reason for the loss in performance.