Warframe appears to be another game that gets monstrous gains with FSR + Resizable bar. With these enabled and FSR at the usual 'ultra quality' input resolution of 2954 x 1662 upscaled to 4k, I was seeing about a 250fps average on max settings with the DX12 Enhanced engine running on vkd3d. The game runs butter smooth.
Note: This video is aimed at displaying performance gains while retaining image quality, however it is a 4k capture downscaled by my capture card to 1080p video, so video compression/quality will not fully reflect how it looks in native 4k. If you would like to see image quality, here are some 4k screenshots from Witcher 3 which display FSR working to retain image quality while upscaling:
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