German tech site ComputerBase analyzed the impact of HDR in combination with 4K resolutions. One of the conclusions seems to be that switching on HDR hurts performance
more on NVIDIA cards than on AMD models.
Hexus interpreted the results in English over here:
Nicely we also have an average overall chart to share with you, above. You can see with the baseline set as 100 per cent for the GTX 1080 running games at 4K HDR, the RX Vega 64 scores 110 per cent. Turning off HDR results in 111 per cent performance for the Nvidia card, and 113 per cent performance for the AMD card. You will note therefore that turning on HDR has a bigger detrimental performance impact on the green team hardware, on average.
The reason why AMD fares better with HDR is unknown. It could be related to how NVIDIA converts RGB to reduced chroma YCbCr 4:2:2.