When I learned what bullet chess was I thought about a similar topic. I thought doesn't the speed of moves more depend on the skill with using the mouse and mouse tuning? I think it very much does which is why I view bullet chess as kind of pointless as your thinking speed will always be bottlenecked by your ability to use the mouse fast. However, if this were done on a touch screen such as maybe an iPad or microsoft windows touch screens, it should be no issue if the player can move their hand quickly enough. They can just hold the hand close to the screen for game duration.
To answer the question itself, you might get faster mouse movement if you buy a Logitech gaming mouse and make sure to install their software. There are settings for pointer speeds as well as accuracy. (I've only had experience with Logitech gaming mice). I also doubt that increasing the pointer speed beyond that which windows allows will make anything any faster. It moves very fast if you turn it to maximum and practice. I'd have more trouble with aiming.
How do the people move so fast?
I always lost 2/3 seconds/move with the mouse. Any special mouse or settings to move faster? Now, for me is imposible to play bullet.