Ok I found something I wasn't afraid to install. There's an MSI driver disc on archive.org (uploaded 2016) with version 4.2.0 of Afterburner on it, and it comes with Rivatuner 6.4.1. I installed it on XP and I'm getting an fps readout, which is all I needed.

I do have a zipped up version of RTSS 7.3.3 with registry entries (.reg file) indicating install location that I made for myself for avoiding installer that runs MSVC redistributable installer, which I install on my own. I also have both ZIP and installer for MSI Afterburner 4.6.3. I must have misplaced RTSS installer somewhere as it's not in the same place as the others...

Noticed this topic a while back but didn't realize it was about RTSS, rather annoyingly RTSS download page still lists Windows XP in system requirements so I thought it was still ok.

I did have 7.3.4 Final already installed and simply making a copy of the install folder seems to work just fine without any registry entries, but if anyone happens to have the original installer of 7.3.4 Final (build 27560) I'd appreciate if you could upload it somehere. I'd rather archive that than a copy of the install folder.

EDIT:

Found the installer. I knew RTSS was part of MSI Afterburner but since I don't use that I thought RTSS functionality was built in, but turned out Afterburner just comes with RTSS installer and they run in paraller. Since you can still find the last version of Afterburner that works on WinXP (4.6.5) I downloaded it, extracted the installer and there it was, RTSS 7.3.4 Final installer.

So if anyone is looking for it you can just download MSI Afterburner 4.6.5 from here extract it with 7-zip or something and find RTSSSetup.exe in there. Or simply install Afterburner if you prefer.