I was trying out FSR4 on my RX 6800 XT, Fedora 42. Works really well and it easily beats FSR3 in visuals even on Performance. It does have a significant performance hit vs FSR3 though but it still works out to be a bit faster than a native rendering on Quality.
Yeah I just wanted to illustrate that with some numbers :)
It’s a bit counter-intuitive that frame generation is worse the lower your base frame rate is. And Nvidia in particular has no interest in making it clear that this tool is only really good for making a well-running game run even better, and is not going to give your 5070 “4090 performance” in any meaningful way.