I experience stuttering as well every now and then when my game is locked to 60fps while it could refresh at a much higher framerate. I set fps_max to let's say 90 then which makes it go away in windowed mode.
There's something in the manual about that as well:
Some hints for decreasing the frame rate in your games
Why would you want to decrease the frame rate? There are three reasons. Your script functions might only work properly within a certain frame rate range, and fail at 1000 fps. You won't want your application to consume all the CPU cycles. And most important, you want to avoid stuttering. Stuttering means a camera and actor movement that appears unsteady. It won't be noticeable in a game with complex levels and medium frame rate, but mostly in games with almost empty levels, little content, and consequently very high frame rate that is then capped by fps_max.
The main reason for stuttering is a coarse PC scheduler resolution that leads to inaccurate task start times, especially when many tasks are running on a particular PC. This problem can be avoided by limiting the frame rate not only with fps_max that just gives task time back to the Windows task scheduler, but by really burning CPU cycles in some or the other way. Fortunately, this is easily done. If your game experiences stuttering, just place some more details in your levels for avoiding a too-high frame rate.
