I often play Doom3 and HL2 with the 'show fps' options turned on. There are times where it's reporting 120+ FPS and I'm STILL seeing jerks and lag and general stutters. Anything below 60fps sometimes hurts my eyes because of all the tiny jerks and stutters I see. Generally unpleasant to play between 32-60 FPS. Would anyone know why? Maybe my monitor doesn't refresh fast enough to display fluid motion?
Monitor is a 2-3 year old KDS 17" X-Flat 1280x1024 60hz. I always play at 1280x1024.
Try setting the refresh rate on your monitor to its highest setting and turning on VSYNC in the game. That should keep everything synced up and reduce some of the jerks in the graphics. If you are still seeing the jerks, maybe your system is having some problems somewhere. I know my 7600GT would run Doom3 just fine and I have very sensitive eyes. Never tried HL2 but CS:S also ran just fine.