I've had two PCs compatible with Windows XP, in both cases, NVIDIA drivers left something to be desired. The old one had GeForce4 MX 440, the newer one has GeForce GTX 750 Ti.
Newer drivers on older card tanked the performance in games, with newer card, monitor settings in NVIDIA Control Panel were bonkered.
Chromium based browsers may have trouble with certificates on XP, if you haven't noticed in Certificate Manager after updating certificates, there are number of them that XP doesn't understand. When my bank still used personal certificate for identification, it was impossible to login on XP. Unknown if --ignore-certificate-errors would help. That was in pre-Supermium time when the best Chromiums for XP were Chinese forks. Mozilla based forks were fine in that regard. I forgot if I eventually just put --ignore-certifcate-errors on every Chromium's launch shortcut, so not sure if Supermium somehow works better out-of-box on XP these days, it's been a while.
Things are broken left and right on XP in my experience. I've had a bit better experience with XP x64, on x86, even my motherboard's SATA controller driver (for working AHCI mode) just crashes. I got an older version of KeePassXC Browser Extension to work on Serpent, it can communicate with KeePass password management program with right plugin, but the whole thing refuses to work on x86 in any browser due to some missing crypto stuff. And for some reason Korean hieroglyphs aren't rendered in AIMP, despite having the extra fonts installed. On the other hand, DirectSound hardware acceleration refuses to work at all on my Audigy Rx on XP x64.
Not sure if these are general XP SP3 problems or something bonkered with Integral Edition specifically, I have more conservative (less updated) variant of XP x64 updated in 2011.
Also, I want my BIOS clock in UTC! XP's also broken in that regard. While RealTimeIsUniversal setting exists and can be added to registry, it's broken, you have to run something like Meinberg NTP service to prevent the displayed clock in the OS to reset to UTC baseline every hour. And setting clock in the OS with that setting enabled still won't update it in CMOS and the displayed clock will reset again after putting PC to sleep, the UTC offset isn't applied on resume. So in my case, the clock goes back one or two hours, depending on whether DST is in effect. Why do we still have this clock adjustment every half-year? So stupid.
Performance in general? I mostly notice it to be better with modern Windows versions. There are some specific things that could be smoother on XP, some old GUI GDI applications maybe. Also Flash Player...maybe something about its D3D9 path, it uses D3D11 on modern Windows.
I do get random sound dropouts on XP while not even doing anything demanding, it can be triggered by something as simple as minimizing a web browser. It takes some load before audio starts to suffer on Win10. And I have an ancient AMD Phenom II X4 920 in my computer, which isn't exactly speedy! Some guy recently pointed out audio glitches in old 3D era GTA games, while he had them on both XP and 10, I only heard them on XP on my computer. At least that was the case for GTA: San Andreas.
I tried running Interstate '76 (a 1997 game) using its windowed mode not too long ago, it uses plain GDI in this case (with its code adjusted to cap frame rate to mere 20 to avoid physics glitches), both on Win11 23H2 and XP (x86 or x64), with CPU downclocked to 800 MHz. I was surprised to see the game run smoother on 11, I expected about equivalent performance. So the more bloated Win11 still got more out of the lower clocked CPU. Maybe compositor (DWM) makes a difference? I don't have the exact numbers since readily available tools only work with hooking 3D APIs, but the difference was considerable to not really need the numbers to notice.
Take any D3D game, run it in windowed mode, then put its window on secondary monitor. See what happens on XP. The frame rate drops considerably. I find this to be even more bothersome with web browsers. Guess what NVIDIA's Multi-display performance mode was for? In its default state, it made OpenGL acceleration work on any screen. It wasn't relevant anymore with Vista.
My honest answer is that I don't know how to make ANYTHING suck less on XP.
For web browsing, it would usually be Serpent with Classic Theme Restorer and Supermium for broken sites. I generally prefer Pale Moon's interface, Serpent just stayed since I migrated from old Firefox 51 years ago to Basilisk before eventually landing on Pale Moon, closest match is New Moon 28 on XP. Serpent has theoretical compatibility with Web Extensions, though not sure how much works with it, very little by my limited experience.
