The easiest way to benchmark Serious Sam is go to to the Demo screen where it gives you all of the choices for the demos. Go to the
console "~" and then type in "dem_bprofile=1" (without the quotes). Then hit the Karnak demo and it should run. At the end of the demo, hit the "~" key again and it will show you your FPS. BTW....run the Karnak demo because it seems to be the most intensive demo. Good luck! If you have any more trouble, just give a holler!
jcwagers