So you did :
host_framerate 500
startmovie
got a shitload of .tga files
synced them with the audio
compiled to .avi


That's what I'm guessing? I mean, I'm not trying to shit over it but the only reason that people render videos at an fps higher than 120 is for the slowmotion parts, so they can have it at a relative FPS. So if you had a bit that was going at 50% of the speed, and you wanted that at 120fps, then you'd record the entire thing in 240fps so when its going half speed, you'll still be getting a high framerate.

I honestly don't think it's worth the effort to get such a high FPS, especially as I doubt that many people have 500hz monitors anyway.