For the best performance, make sure you are updated to the newest version of your video card drivers, and have killed all third-party programs, especially antivirus and video recording software.
If you have the Steam version of the game, then a newer (testing) build might give you better performance. This will come at a cost of a little bit of potential bugginess, since these are pre-alpha versions of the game. Those builds also have additional performance-enhancing debug options that might work well on your system.
The "advanced_testing" build is the release candidate for the next alpha. There will be some testing done on it, but it is not "release quality" yet. It may have additional features and optimizations.
The "internal_testing" build is the nightly build, and has no guarantees of being stable or tested. It will have the latest features and latest optimizations.
If you install either of these pre-release versions, make sure you file bug reports when you encounter problems - See
http://wiki.wolfire.com/index.php/How_T ... Overgrowth
Instructions for opting into unstable/newer builds on Steam:
1. Go to your game library
2. Right click the name of the game (in the list on the left)
3. Click on "Properties"
4. Click the "Betas" tab
5. Switch the beta that you are opting into from "NONE" to "advanced_testing" or "internal_testing"
6. Close the window
7. Wait for the new game updates to download
