That's a good question actually, never really ventured into ultra performance because of past experience with it being really poor so had no reason to check it out since.
I gave it a try just now and actually it's very very impressive at Ultra Performance. In Performance the fps is 60+ but the render/input latency is massively obvious so that's a no-go when path tracing at 4k res.
In Ultra Performance there is just some slight temporal fizzle on things like hair/beards when you look for it, but otherwise at 5160x2160 path traced with DLSS Ultra Performance without Frame Gen I can get 85fps, with Frame Gen enabled that increases to ~125fps and it looks very good. The only thing is that whilst the framerate is higher than 3440x1440 DLSS Quality, I can tell that the input latency is still a bit higher at 5160x2160 DLSS Ultra Performance but nothing too distracting that you would not get used to I think.
There is zero image quality difference when static or in motion with Frame Gen on vs off. I am using DLSS dll 3.6, and Ray reconstruction dll 3.7. Frame Gen dll remains 3.5.10.
There is noticeable sharpening filter halos when pixel peeping the Ultra Performance image, look at the blue doors in the background, the door numbers are the most obvious. Ultra Perf also has detail loss on the vertical pattern on those same doors that are visible on the Quality screenshot, although again, have to pixel peep to notice it.
IMGslider:
https://imgsli.com/MjUwNTQx/0/2
I put in the 3440x1440 one in there too just for a rough guide but I did not rescale it so when you zoom in comparing against the 5160 slides, the scaling is done by the website which appears to be nearest neighbour so you will get more stair stepping , so only use that as a guide for reference detail.
In person the 3440x1440 DLSS Quality FG On, the performance is more responsive at ~108fps vs 5160x2160 DLSS Ultra Performance FG On which gets 120+ fps due to the difference in PC render/input latency. The input latency is reduced greatly if I turn off Frame Gen at 5160x2160, but that then reduces the framerate to about 80-85fps which is noticeably less smooth in camera motion than with it on, but the upshot is input latency is eliminated. This is a trade-off some may opt to make if they must have 4K.
Personally I will stick to 3440x1440 DLSS Quality FG On as that hits the sweet spot for input latency, framerate and image quality.
Some 5160x2160 screens to see the LoD up close: