How to increase mouse size by velocity?

[Ofnuts]

Technically what you want would be done with one of the "Brush dynamics" that links the brush size to the "velocity" of the pointer.

However, if you are using a mouse, this won't work well, because the pointer movements on the screen are not a linear map of the mouse movements on the mouse pad. If the mouse moves faster, the pointer will move even faster, this is called "mouse ballistics"(*). Try this:

• put two heavy things (books) on your mouse pad with about a hand's width between them
  
• tuck the mouse against one, and move it slowly until it is against the other. See how much distance your pointer has move the screen
  
• do the same but jerk the mouse quickly. The pointer will have moved a much longer distance (it is likely against the screen).
  
• you can also try to sign your name with the mouse... see how hard it is?
  

In other words, these options are really meant to be used with a tablet, which is designed to map "linearly" the pointer moves to the stylus moves.

(*) This why mouse pads should be used in "portrait" mode, because you can move your mouse laterally a lot faster than "vertically": you need less horizontal room, and your portrait-mode mouse pad maps to a landscape mode display.