I have released the latest and final (at least until there are new tiles) version of this mod.
The new version contains the same Medium detail tiles from the prior version, but also contains a new set of Low detail tiles, which are more reduced than what I'd released before. Unlike with the Medium detail tiles, I decided to wait until I was completely finished before releasing a version with the Low detail tiles, so there will not be any more versions. It's safe to go ahead and start a new game using these.
Also included in this new version are some tips about improving performance through options, and also about frame rate limiting (it goes into more detail than my post earlier in this thread; also, I still don't have any info about an ATI frame rate limiter).
With the Medium detail tiles, I was trying to make changes that you wouldn't notice, but would still improve performance. With the Low detail tiles, I threw caution to the wind and just removed a lot of stuff, so you'll probably notice the difference. I figured, as long as it still resembles the original tile, that's good enough.
With any luck, this will prevent your computer from cooking its surroundings. Maybe it'll even save you money on electricity.