Well, haven't seen this kind of advice anywhere maybe I'm wrong, but here it goes.

If you have problems with TB running slow. and you have a multi-core processor, try either of these:
a) -Go to your graphics card's control panel (I use NVIDIA, Ati users, try doing something similar)
-Click on Manage 3D settings (it's on the left side)
-Click on Program settings
-Click on Add
-Go to your toribash install folder and select tb.exe
-Now with that done, scroll down, and turn "Threaded optimization" off (for tb.exe)

If you can't do the one above, I'd recommend the following:
b) -Each time you start TB, go to the task manager (ctrl+alt+delete)
-[WIN7] Click on "Show processes from all users"
-Right click TB.exe
-Click on "Set Affinity"
-Deselect all cores expect one of your choosing (I'd choose something else than CPU 0 if I were you, for reasons I'm too lazy to write down here)
-This has to be done every time you start the game's executable, since affinity settings aren't saved by windows.

Voila, you should experience a significant boost in your framerate.