0.63 @ 1600 / 1.25 @ 800 / 2.5 @ 400
I seem to rotate between these which are all theoretically the same so muscle memory stays the same but each feels different thanks to pixel skipping which means i can shake it up if I'm not feeling it.
Rather than just lowering to 400 tho you should find out your mouses native dpi and play at that, it'll be much more accurate in line with your hand movements. You get so much pixel skipping on loads of mice at 400dpi.
That said if you're using over the native DPI (which is usually max 1600 on most common mice) your mouse will introduce interpolation which will make things more inaccurate!
Also make sure your windows mouse sens is set at 6/11.
TLDR: Find out your mouse native dpi, play at that for best performance, adjust in game sens to suit new dpi.