Vsync off may increase performance but you will see weird missallignment of graphics.... The option is in lewpy's pluggin in the options.... Petes pluggins don't have the option but, your graphics card drivers should have an option to turn it off or on.... Right click on your desktop and check properties, settings, advanced........ and see if you can turn it off and on... In my experience, vsync off didn't really make a huge difference...... The difference is noticeable in PC games though.... but not very much on epsxe.....
Are you using Petes Plugins D3D or OGL? If you are, then Pete has reccommended that you turn off VSYNC. VSYNC is a function of your video card. You'll find the option to change it in your video cards controll panel.