I just installed the s3tc textures and edited the ini file, and honestly I'm not that impressed. I did notice the walls do look much better on some maps, but I don't think it's worth the hassle of having to adjust your gamma and brightness way up in the detonator drivers...(the one in the game doesn't seem to work anymore, and believe me, it's dark as hell if you don't adjust it)
As for speed, it does give a couple more fps according to the timedemo thing, but it stutters when there are other players on the screen. Direct3d still runs better IMO, and I'm switching back to it. I hope they'll fix it, because it does have really good potential, but it's not perfect yet...
Forgot to mention, did you look at the sky in the galleon map, it's just horrible.