I think I got it, here's what I did:
It's set to compatibility mode for Windows XP (Service Pack 3), and run as Admin. With either of those unchecked it will fail to start. Once in the game, I went into the settings option, and under graphics, I selected the drop-down where its says "Select Renderer" and changed it from "Primary Display Adapter" to my graphics card (was the only other option available; the computer in question has a single graphics card) as it was explicitly listed there. I also clicked "Direct3D" instead of "Direct3D TnL Hardware" (no real reasoning behind this, just what I did). Set it back to my monitor's native 2K resolution (it was at 1280x1024 before, to try and get decent performance), all other stuff was at max, loaded up the save that had been giving me trouble (a campaign map with 3 computer players and a lot of units and water) - it not only looks to be running smooth as glass, but the visual quality of the water and fire effects seem to be better.
I'm theorizing that it was, for some reason, defaulting to CPU rendering (there's really no other options here - I don't have multiple graphics adapters in this system; it's either the CPU or the Radeon), and the CPU was okay until it got into very high resolution with a lot of objects on-screen (e.g. the game was fine at the start, but as me and the AIs build up bases, it would slow down, I'd lower resolution, it'd go fine for a while, and slow down again). I only theorize this because a few other older-games have, in the past, defaulted to the CPU - and it does alright as long as things don't get overly complex.
Oh I should also note, it crashed when I set it to the graphics card, but when I restarted it, it retained the settings and that's when I tested it. I'm not sure why it crashed or what significance that had, but figured it was worth noting as well.
If anything changes (e.g. it stops working again) I'll certainly post back.
Some random side thoughts:
- I remember years ago playing this game on multiple monitors on a GeForce FX using the "span" mode within nView, and it allowing you to select that combined resolution in the settings without much fuss. I'm not sure how it would translate to SoftTH or similar, and I'm not likely to investigate that on this computer (the monitors it has do not line-up either in resolution or as they're setup on my desk, so multi-monitor rendering doesn't end up looking so great).
- The game appears to be Vert- (WSGF claims this as well, but their overall information about the title seems very limited), as the view-port seems to "shrink" at higher resolutions. I don't have any solution for this (and it may not be fixable); in theory running it at a 4:3 resolution and letting the graphics card scale it would be workable though.
- In theory it should allow you to select whatever output device you want, if your system had multiple graphics cards, which could be useful depending on your hardware configuration and desires. I'm not sure what it's bottom-end performance requirements are - I know that my Pentium 4 with a GeForce 2 MX ran this game when it was new, but I do not remember what settings (at absolute maximum it would have been 1280x1024, because that's all my monitor at the time supported, but more than likely it was 800x600 or 1024x768 to ensure a higher refresh rate).
