Yes, I'm aware of the fact that HDR and AA apart would produce an FPS hit separately, and that therefore they'd both impact perfromance together, but when I use them both (by forcing AA from my graphics card), magic effects and fog "bunches up" -- instead of diffusing mist for fog, for example, it's a few will-o'-the-wisp-looking globs that glow like mad and drastically reduce FPS when viewed.

If this is a common problem I've never heard it mentioned.

Forcing effects always has the chance of causing anomalies.

There are also certain GPUs that do weird things when you force the effects. What's your GPU?

Oh, yes, that would be helpful, wouldn't it?

Let's see. Nvidia GT 420M, if I'm recalling correctly. That's on a laptop. I have a desk computer with a GT 220, and I believe that it has the same issue.

If it's specific to Nvidia cards, no one's ever mentioned it. Perhaps I'll fool around with specfic settings later.

Also, any texture replacers?

None whatsoever.

I assume things look fine when you turn off the forced AA?

If by "fine" you mean "everything that's not fog has jagged edges but is otherwise okay," then yes.