In terms of accuracy:

you want to stay on 6/11 on windows sensitivity or drop down to like 1 or 2/11. Reason being is that 6/11 means that 1 count from your mouse is 1 pixel on the screen. If you change that to higher or lower, you will certainly end up with rounding errors. Likewise you want to turn off precision/acceleration so that you develop muscle memory of where the mouse is on the screen. having a nonzero acceleration means you have to do an extra calculation in your head on where you mouse is going to end up. And it's not even a calculation, but a "guess".

At low windows sensitivities, you can still touch every pixel (which is impossible on sensitivities 7+) and you're using your high CPI to make it manageable. I'm not telling you to do this:

(i actually think this is a bad way to play since he can't turn around)
but actually using your mousepad makes you more accurate in the long run. If you only mover your mouse 1 cm^2 to get from one end of the screen to the other, then the slightest shake in your hand will cause you to miss. If you move 5 inches, you're using more muscles, and you lessen the effects of random hand movements.

Switching DPI between games is okay, but if they're the same resolution, you probably want to use the same DPI.

Also note that when I say DPI I mean pixels per inch, which is your windows mouse rate * mouse cpi. It's a pain to re-learn how to use a mouse, so you may as well do it now if you agree with my logic here. I went from 4800 DPI to 450, and I've definitely improved in some aspects, but fallen in others (which are bound to come with time).

I was talked out of getting a mousepad earlier. Also, playing with that sensitivity would drive me nuts; I don't think I'd ever get used to it. Also, my desk is small, so I don't have a ton of room to move my mouse around, anyway.

Like I said, I haven't adjusted the windows sensitivity (it's on 6). Acceleration is disabled.

at 1920x1080, I would use 1600 dpi max.