<< got a source? or better yet, a demo? i dont have any that compare beyond 60 (well, it will compare 70 to 35, or 80 to 40, etc.) >>
The problem is that the ability to perceive the difference between framerates varies from person to person. I sure as hell can see the difference between 60 and 120. Shoot, I can easily see the difference between 80 and 100. But this is certainly not to say that anyone else can see it.
edit- I think Quake 3 would be a good demo for this, as you can tweak the maximum FPS by a setting in the console (com_maxfps). If you have this game try first setting com_maxfps to 60, then to 120, and move around after changing them back and forth.