You could really use an upgrade, yeah. Let’s see what ces brings.
Input lag doesn't depend on the game's native resolution, but for your hdmi 2.0 tv ; it depends on what you set your console to output.
1. If your console outputs 1080p, the x1 extreme chip has to upscale that to 4k. Causing 40ms lag, but slightly nicer picture vs 4k output because of the quality upscale, but for hdr, more importantly you retain 4:4:4 chroma (less banding, better color) in hdr.
2. Output at 4k, and your tv doesn't have to upscale, but you can only get 4:2:2 chroma in hdr, making those titles look worse, but you get 24ms lag, which is basically a whole frame faster. If you already do this, the jump in lag you'll get going to the x90j won't be huge.
Pick which is more important to you, and set your ps5 accordingly.
For x90j, I guess it's possible they patch the vrr over the years, but remember Sony already has your money. I wouldn't expect it, and they can't patch in more zones haha. Motion is what it is from day 1, they're probably not patching that even if they could.
For example, if you bought x900h in 2020 on Sony promising to patch vrr, you'd be sour to see vrr disabled local dimming!