I came up with 4 options:
1) Upgrade the OS so I could upgrade Lightroom so I could read the photos off the OM-1 and lose the older 32 bit programs.
2) Not do anything and wait for a faster iMac than the 2021 24" M1 iMac. Wasn't sure if this gap is ever going to be filled by an upgraded Mini or an iMac (PRO?).
3) Buy a refurbished 2020 27" iMac and use it for another 3-4 years until the Apple desktop lineup is settled.
4) Buy a Mac Studio and monitor.
I went the 4th option and will keep the 2013 iMac for now. The 2020 Intel iMac would be a fine short term solution but future OSX versions will not be fully implemented on these iMacs. Gave up on the future 27" iMac, not sure if there is room between a M1 PRO/MAX Mini and a Mac Studio.
It's a shame, the 2009 27" Imac is what got me to leave Windows.
Interestingly, I was in a similar boat - always wanted a Mac desktop (had a laptop), kept putting it off, figured I would get one after the Apple silicon transition.
Instead, a few weeks after they launched the Mac Studio and the 27" Studio display, I went with your option 3 and bought a low-end (with 10GbE) refurb iMac. Slowest i5 CPU, 16 gigs of RAM (that's what the model with 10GbE available in the refurb store that day had - completely pointless since I always intended to put way way way more RAM in it), 256 SSD (which I could have gotten a 512, but again, there was no 512 with 10GbE in the refurb store that day). Quite a contrast to my 16" M1 Max, eh?
My thinking: it was CAD$1859 + tax + AppleCare. Plus the extra RAM I've put in it. A Studio Display, with the normal glass/stand/etc, is CAD$1999. There aren't really any other options for a retina screen (and sorry, but if I want low-resolution, I'll use my Windows machines, thank you very much). Assuming I wanted at least 64GB of RAM, that puts me at a minimum of CAD$2999 for the Mac studio. And that's for a base model with just the extra RAM. Oh, and I was forgetting the fact that the Mac studio doesn't come with a keyboard/mouse while the refurb iMac came with 'good enough' ones - so, add CAD$229 for the (better) keyboard, CAD$119 for the mouse or CAD$169 for the trackpad, and... that's another $350+ CAD.
So, my Intel iMac cost me ~30-35% of what your option 4 would have cost me. For what I do with it, it's more than good enough. And sure, I expect the last version of macOS for it to come out in 2025 or so, so its life will be less than a Mac studio's, but... if I've spent 30% of the money for a system that lasts me half as long, I figure I'm still ahead a little bit?
(Part of my thinking, too, is that I think the studio display is massively overpriced for what is the same panel that the Retina 5K iMacs have had for the better part of a decade. And there is no other option, for now, other than the pro display XDR)
That being said, I do wish it had touch ID...