And it works fine. If it didn't, I wouldn't be able to use my computer at all.
This is the statement that makes me, as a computer technician at heart, hate people.
Just because it boots does not mean it's fine.
Those temperatures are not normal. Thus that card is not working normally.
Why the hell is the temp so Armok-damn high? I'm not trying to render Crysis here. And why that would affect DF in the first place is beyond me.
Since you didn't hear or didn't care about what I said the first time,
here's essentially the exact same thing I said three pages ago, in different words.
Computers can't deal with heat.
They don't want anything to do with it.
Thus, if their components start heating up beyond safe values, they will shut those components down to reduce the amount of heat produced.
This will cause things to run slower, naturally.
A failing graphics card, depending on the circumstances, can start generating obnoxious amounts of heat. Of course, they can produce obnoxious amounts of heat to begin with.
My old 8800GT idled at 80C. That's considered a normal temperature for that card, however. It never topped 90C. It's fine.
Your card is running at over 100C. That is most certainly not normal, and probably dying. You won't notice much difference in daily operation (the games you've listed that aren't having the problems are fairly new, they'll spread the "love" to multiple GPU cores, whereas DF can only use one), but if you keep pushing it so that it's shutting itself off (this slowdown issue is a result of throttling to keep the heat in check) you'll almost certainly damage the cores.
Not to say that they aren't damaged already.
Yes, I was talking about multiple cores in that paragraph. Because any graphics card you can buy today has more than one.
In this case, given the circumstances you're describing, I'd say it's something in the card controller though, as it doesn't seem to be shutting off the cores when it should be.
...
If your graphics card is hitting 120C (we use Celsius in the computer world, for the record) something IS wrong with it. No two ways about it. They just don't get that hot before they shut off completely.
The hottest temperature I have
ever seen in a computer was 100C, on my current processor, while I was
stress-testing it (creating obnoxious amounts of heat intentionally), using an
inadequate cooling system (not getting rid of the heat quickly enough). In that instance, the "magic number" is 80C. It will start slowing down my cores at that temperature as an attempt to keep the temperature down.
Lots of words, all of it information. No tl;dr for you.