Vertical sync is a horrible idea for ESF because it places a very small but very noticeable delay on your movements as your video card redraws those extra frames to make sure nothing is tearing.
Also, if you want to get technical, the size of your hand and the flexibility of your wrist, along with the sheer size of your mousepad and whether or not you have a corded versus an optical mouse all affect your sensitivity. There is also a function inside of windows that determines how many signals it will recieve from your mouse at any given time, and with the proper utilities located off of the internet, you can increase said reception (similar to increasing your monitor's refresh rate) to improve response time. It's also impacted by your natural hand eye coordination.