Basically title.

Wondering if the fps loss are worth it and a quality comparison.

Has anyone found a video or ran the test themselves?

4.5 tanks a bit more of performance but looks so much better

At 4K Ultra Performance, 3.8 is terrible, 4.0 is okay (depending on the game), and 4.5 is actually quite good. Personally, I would still try to use Performance mode with Preset K (4.0) instead of Preset M or L (4.5) with Ultra Performance.

Same

When Ultra Performance was first introduced its intended usecase was output in 8k.

With DLSS 4.5 it looks okay at 4k. There's really a lot of quality difference.

But Ultra Performance works well at resolutions higher than 4K. I use DLSS Ultra Performance with Preset L in Anno 117 at 5120×2880, which means it's upscaling from 960p to 5K.

Problem with sticking to preset K is that ghosting persists. My workaround to claw back the performance hit with using preset L is to use a custom scale percentage of ~44% so I gain the benefits of L at the same time like better reconstruction of pixels, reduced ghosting, and better motion clarity.

Preset L at 44% looks sharper than K at 50% (Performance).

It depends on the game. I really like Preset K, and I usually don't run into ghosting issues. I also don't like how oversharpened Presets M and L look. In some games, they're completely unusable.

That said, I enjoy tinkering and finding the best preset and resolution for each game. OptiScaler is perfect for that. It lets you change presets and resolutions on the fly, making it very easy to compare them.

Tried in Plague Tale resonance.
UItra pefrormance at 2160p >>> DLSS Quality 1440p.
Much cleaner , sharper and detailed

Hardwareunboxed has a video comparing 4 and 4.5

Does this work very well with DSR/DLDSR?

not bad, but still not good enough for me.

No idea. I've never used that.