As I understand GPIO speed is limited and below usb 2.0 speed if I am not mistaken. So what is the maximum speed of this setup? How ‘gaming” gaming mouse can be?
Even with a non polling mouse there would be no point in reading the result more than a thousand times per second. If you move the mouse 3 inches per second (quite fast) and you only process 1000 reports a second you would still achieve a resolution of 0.003 inches.
Despite the USB protocol overhead, it is plenty even for a gaming mouse. Pretty sure there's no point polling it at above 1 kilohertz or so.