So it seems like you've done, in a way, the opposite of what I did. I also recently bought a 5,1 for... quite a bit less than $300USD... and the original owner had gone full out. 512 gig Apple SSD, 64 gigs of Apple RAM, 2x5770s, dual 6-core Xeons. Must have cost upwards of $8000CAD new? I threw in a random hard drive for Snow Leopard but otherwise I haven't upgraded anything.
My goal was to have a collectible machine that could bridge the gap between a G4 MDD and my 2020 iMac. I originally was thinking about 2011 iMacs, but people here advised against them due to unreliable GPUs. Same with the Mac mini with the discrete GPU.
And so that means I'm stuck with the 5770 and High Sierra. I've actually found High Sierra less bad than I was expecting - I have two current web browsers (not for much longer), for one thing, and a version of MS Office new enough that it can connect to an O365 mailbox. And Steam still works...
But at the same time... what this reveals is the limits of Apple's OS policies. A few weeks before, I dug up a C2Q from the closet, upgraded it from a Q8300 to Q9650 from eBay, and set it up to dual boot XP and Windows 11. (Ironically, it also had a 5770, though I replaced that) Officially, of course, that machine is unsupported for 11. Unofficially, it works just fine and you can run the current version of Office, current web browsers, current version of Steam, etc and you will be able to do so for at least 3-5 years longer. This is a motherboard I bought in fall 2008, now on its third CPU. My 5,1 Mac Pro has 8x the RAM, substantially more CPU performance, a factory SSD, etc, and yet it's a few months away from no longer having a current web browser, it hasn't received an MS Office update in... oh, I dunno, at least three years, etc. And a number of apps I use heavily on my more current Macs - Infuse, Fiery Feeds, etc, all of which have strong iOS/Catalyst/etc ties, don't exist at all in a High Sierra-capable version. That machine would be so much more capable if I could put Monterey or Ventura on it - really, if it had Monterey or Ventura, it could be a daily driver Mac instead of an experimental/collector item.
This also reminds me of a depressing thought experiment I did in another thread. If someone, in late 2005, had bought a Dell with a Pentium D running XP, assuming they formatted their hard drive once to go from 32-bit to 64-bit Windows, they could be crawling Windows 11 (unsupportedly) and a modern web browser well into the second half of the 2020s. It wouldn't be pretty or particularly usable, but it would work. The same person, had they bought a Power Mac G5 (which, especially in its dual-processor models, probably outperformed the Pentium D) on the same day, would have lost the ability to have a modern web browser in, oh, 2011 or 2012?
