I was getting mouse lag, so I turned vsync off (by changing ipresentinterval to 0). Now everything runs too fast. Smoke billows too fast, my player and npc's walk around too fast etc. Any ideas?

Win7 64, GTX570, i5-2500cpu, 8g ram

try this: restore ipresentinterval to what it originally was (sadly I don't know what the default value is). Now launch the game and, before pressing 'play', go to your settings options and look through the settings windows until you find a checkbox for vsync. Uncheck that box. This should turn vsync off the way F3 expects it to be. If it still is having problems, change your mouse senstivity in-game (after pressing 'play') through the in-game settings options. Still problems? Make sure iFPSClamp=0. Still? Try iFPSClamp= (some value higher than 60).

Why I think iFPSClamp works inverse of how you rationally think it would: I once set iFPSClamp=4 to try to get FPS to a crawl for debugging purposes. Instead of slowing down, game speed went through the roof, actors talking speed was like the chipmunks, motions were lightning fast and got out of sync with scripting and the game stalled. In the delivery room my baby cart ran into the back wall and stayed there until I force quit F3. When I put iFPSClamp=0 again, everything went back to normal.

Thanks! Making progress finally!

I knew I needed some kind of fps limiter. You're right that iFPSClamp seems to be inverted. I tried 70 and it was still too fast. Tried 120 and it was too slow. Right now I'm at 90 and good to go. But I wish I knew the exact number to use so that it runs exactly how it should. Oh well, this is good enough for now. Thanks again.