That's a pretty low screen resolution!
It'd documented in the manual if you search for "framerate":
In fullscreen mode, DirectX keeps the frame rate always in sync with the monitor frequency between 60 and 80 Hz in order to avoid tearing artifacts. The screen refresh is artificially delayed for matching the time when the monitor has finished its video cycle. This delay is visible in the 'screen refresh' time in the [F11] panel. Thus you'll never get a higher frame rate than your monitor can display. Your frame rate will be an integer division of the monitor frequency (such as 60, 30, 20, or 15 Hz when the monitor frequency is 60 Hz). When the frame rate is close to the monitor frequency, a small change of the rendering time will cause the frame rate to suddenly jump from 60 to 30 fps or vice versa.
Here's the deal: A lot of games let you use an option called "vsync" -- or "vertical sync", where the next frame doesn't begin to be drawn until the last frame has finished being drawn. When this is
not enabled, you often get something called "screen tearing", where part-way through drawing a frame to the screen the next frame is calculated and begins drawing.
Mirror's Edge had very obvious screen tearing, probably due to the graphical style.
In A7/A8 this isn't an option: v-sync is always enabled in full-screen mode.
Jibb
