The best polling rate varies. For modern games, 500hz is best, but a lot of older games don’t support polling rates that high, and having it set too high will actually cause lag and be less accurate.

1000hz polling rates don’t matter. Only a robot can tell the difference between a 1000hz and 500hz polling rate, and all turning it up over 500 does is use more CPU cycles. You could actually impact performance enough with 1000hz that it could actually be worse than 500hz depending on your CPU.

One example of a game where high polling rates have a negative impact would be Classic Doom and Doom II, even using a source port like GZDoom the games don’t support more than a 125hz polling rate.

Build engine games are another good example of games where a 125hz polling rate is better, that’s games like Duke Nukem 3D, Shadow Warrior, Blood, Ion Fury, Redneck Rampage, etc…

As for DPI…

You want higher DPI, with lower sensitivity.

You want as much of your effective sensitivity to be hardware rather than software for the best accuracy, with no smoothing or acceleration.

Even with a 16,000 DPI mouse, in some games you will need to bump the sensitivity up a notch or two, but generally you want it as close to 0 as you can get it and still be able to move the mouse around the screen comfortably.

In some cases this might be too sensitive even at the lowest sensitivity setting, but in those cases it is better to lower DPI rather than bump up sensitivity.

In Windows settings having mouse sensitivity at around 50% is generally a good place for it to be. Turn it down rather than up, as low as 25% could be good for some people and some games.

Sensitivity set in Windows is better than in game sensitivity settings for accuracy. You want as few “middle men” that impact sensitivity between your hardware and the OS as you can get.

If a game has a raw mouse input setting, use that.