Since I installed the d3d9.ddl fix I've had a pretty decent framerate. 40 - 60 FPS, but I still had a lot of mouse lag, which made the game feel sluggish.
In your .ini file, find the line that says iPresentInterval=1. Change the 1 to 0. And there you go.
Doing this made my mouse movement a lot more responsive, both in menus and when looking around. This may not apply to everyone, but trying it out can't hurt.
