Gaming

That is for you to decide.

The way you decide is to go to a reputable review website like https://www.techpowerup.com/review/?category=Graphics+Cards&manufacturer=&pp=25&order=date and select one of the reviews of a relatively recent, unrelated card, for example the XFX Radeon RX 7900 XTX.

For this specific site, you then go to the "Average FPS" (or "relative performance") page and look for your models you actually want to compare to in the list. Since you picked a relatively recent review, you can also see newer cards, so you can also see how much of an upgrade you'd get with newer cards you maybe haven't considered yet.

In this case, the average fps of the 5700XT is 49.2, while the 6700XT gets 60, an improvement of ~22%. Now, you either know what 49 and 60 fps look like, or you go into one of your older games and use an fps limiter to limit to those fps values and play a bit and compare.

In any case, the final decision is up to you and no one can really tell you what you think your money is worth.

Edit: of course, this assumes your CPU is not a bottleneck. These tests always go with the most powerful CPU. You haven't said anything about yours, so I assumed it wouldn't be a bottleneck.

CES is next week, unless you get a really good deal, this is the moment to wait and see how the market will shift this year. As for your performance question, I recommend the relative performance table at the bottom of your current gpu's page: https://www.techpowerup.com/gpu-specs/radeon-rx-5700-xt.c3339

I had a 5700XT years ago with a ultrawide monitor and couldnt play games at a decent framerate unless I lowered settings to medium at the highest iirc. Frames over resolution I learned.

For my new pc years later I skipped the 6000 series and currently have a 7800XT with a normal 1440p monitor and I find I still have to keep the settings around medium to high to get good fps (around 80-100 in games like baldurs gate 3). I think the 7800XT is a extremely fair price to performance right now before the gpu market gets bad with tarrifs and nvidia being nvidia.

I moved from a 5700XT to a 6750XT and it was well worth it. It struggled with Cyberpunk 2077 to running it smoothly. The 5700 started having issues with newer titles, but the 6750 is still going strong.

https://www.phoronix.com/review/radeon-rx6700xt-linux/

Based on the 1440p results in that review, I would say that the upgrade might make sense, depending on the games and the price.

It might also be worth finding out whether your games are CPU bound on your system. If they are, maybe consider an X3D CPU instead of a GPU upgrade.

Do you have a specific budget in mind, what sort of games do you play?

I'm not sure what the used market is like in your area but I'd see if you could pick up a 6800XT, 1440p would benefit significantly from the additional RAM. Here I think you could probably negotiate to £350-£370 or so?