Those both equate to different sensitivities.

But use the higher DPI with the Windows adjustment--most 1800dpi mouses that I know of (Deathadder, MX518) actually lose performance if you set their DPI lower.

Don't you also lose precision if you lower the windows sensitivity below 6/11?

In games that use in_mouse -1 style mouse polling, yes. I kind of thought 11/11 was the most precise, but I don't know for sure.

edit: Just checked, 6/11 is full precision, past that is scaled up.

No, 11/11 is least precise. 6/11 is most precise as it's 1:1 movement.

11/11 is also exactly precise as it gives a 2:1 ratio of pixels to mouse counts all the time. You could half your sensitivity in Quake, use 11/11 (from 6/11) and in_mouse -1, and your mouse would be exactly the same (but that would be stupid).

You do, but it's the same exact kind of precision loss that occurs when you set your mouse's DPI lower.

If you change the Deathadder's DPI, for example, from 1800, the mouse will exhibit negative acceleration at a point much slower than at 1800 DPI.

1800 cpi 4/11 is effectively 900 cpi as far as I can tell.

ALWAYS use 6/11 or middle in windows.... use lower dpi in windows if it's too fast but don't ever use anything other than middle... there is something about a ratio that i read a while back that messes up if you don't use middle

look here:
http://www.overclock.net/computer-peripherals...guide.html

check section 1.2

While I can believe that the left/right up/down ratio problem existed for the guy who wrote that, I can't reproduce it. If you aren't concerned about losing DPI then there shouldn't be a problem with using lower settings.