Just pulled out the T43p and upgraded it to 7.3. It’s so slow, with the PATA plater drive and single core; but it still chugs along and so I pull it out every once and again to update and browse the web like it’s 2005.
And of course OpenBSD still runs just fine. It’s probably been half a decade since the XP install was wiped and replaced with whatever the then current OpenBSD release was. I used to pull the bsd.rd from http and boot that from the loader prompt; these days, sysupgrade(8) and syspatch(8) do all the work.
How much memory. Also are you waiting for the kernel relink to complete ?
I have OpenBSD 7.3 on a R51e and it works fine, zippy considering. But of course, Firefox is a no go . It has 2gig memory, but I always wait for the relink to complete :)