That would be caused by vsync, which caps the FPS so it cant go above your set refresh rate. Change your refresh rate in display, then make sure vsync is disabled in your games.
my friend was bragging his computer w/a athlon xp 2500 and nvidia geforce 5200 was getting 20 more FPS in diablo 2. It was cause of this vync thingy i was getting 60 he was getting 80 lol. Now 350+ ez.
With disabling v-sync you may see some image "tearing" as your monitor and graphics card go slightly out of synchronization when the refresh rate exceeds the monitor's abilities.