I found this thread on STEAM forums and put the .dll file in my RAGE folder:
http://forums.steampowered.com/forums/showthread.php?t=2157055
Before I copied this file the gameplay felt sluggish and slow, nothing close to the experience I was hoping for. Now I get about 3x more FPS but I get heavy artifacts but it feels like the shooter it was meant to be.
Has anyone used this .dll with FPS increase without artifacts?