You will find the mouse is jerky after shelling to dos or after changing to a lower resolution mode (implying lower video refresh frequency).
This happens because we had to synch with a higher frequency, it might take a few seconds to adjust to new video frequency.
Video triple buffering is recommended for speed, but it requires 3 times the video memory, for example 800x600 requires 800x600x3 (bytes), roughly 1.4Mb.