Penumbra: Overture sets the refresh rate automatically to the setting you have for your desktop/Windows. Overture also use a LimitFPS command to lock the rendering to 60 frames per second at most. If you want to bypass this you can do the following:

Step 1. Make sure vsync is disabled in Penumbra: Overture -> Main Menu ->Options -> Graphics -> Advanced -> VSync on/off.

Step 2. Disable LimitFPS by editing the settings.cfg file in a text editor. This file is located in /My Documents/Penumbra Overture/Episode1/settings.cfg  locate the "<Graphics..." and change LimitFPS="true" to LimitFPS="false". If you have trouble locating it, use a search/find command to locate LimitFPS.


If for some reason you do not get a result your a satisfied with you can also use the following utility/tool.
Use Refresh Lock to force the game to run at a higher/ lower refresh rate.