I wouldn't do that if I were you. Browsers should be as tough as possible against attacks, and disabling security features is not a good idea.
You can speed up a browser safely however. Disable history and saved form data. Uninstall toolbars and the like. Furthermore, I would dare say the realtime internet protection offered by many security suites is unnecessary, too. Use a strong AV (I recommend the free Microsoft Security Essentials), and combine it with some common sense.