You can define custom resolutions in any GPU driver (NVIDIA/AMD/INTEL) that are way higher than your monitor's native maximum. This is called "downsampling" and is used as a special AA method to smooth edges. Tools like Fraps are recording the graphics card's output signal and therefore the clips will have that higher resolution too.
Larger frames means more information and that will possbly cause bandwidth issues, resulting in your monitor being unable to handle it (I can't make use of downsampling on my laptop due to that). Reducing the Hz will possibly help out on that, just in case. I've done some 2560x1440 recordings at 58 Hz this way on one of my 1920x1080 60 Hz desktop monitors too in a few games (SA, CS:GO & FarCry 3).
This has nothing to do with upscaling and really brings the native image quality. The monitor is simply just resizing the larger image to make it fit.
tl;dr: Check this out if you are unable to define it through your GPU driver.
http://forums.overclockers.co.uk/showthread.php?t=18584921
