You raise the sensitivity of the mouse, you need to drop the sensitivity of the game. High DPI does not = better, 400dpi is perfectly usable with the right game sensitivity.
DPI is only really useful when you need extreme accuracy, and above a certain point, it really doesn't matter that much. High DPI is technically better than a lower one, but unless you're going to be sniping at a 100x zoom, it really isn't needed.
For example, say you had a mouse with 100DPI. This means at a "normal" sensitivity, moving your mouse by one inch would move the cursor by 100 pixels. Now that might be quite slow, so you'd use a higher sensitivity of, say, 3 pixels per dot. Now, one inch of movement would mean 300 pixels of cursor movement - however, the cursor would move in "jumps" of 3 pixels at a time, and if you needed to get accuracy down to a single pixel, that wouldn't work. Now if you had a mouse with 300DPI, you could get the same speed of movement, while also having the accuracy of moving the cursor by 1 pixel at a time. Like I said, this is incredibly accurate and mostly not required. These ridiculous DPI's of 5700 would never be practical at a 1:1 sensitivity unless you have amazing accuracy.
Marc - your problem sounds like what I described (very low DPI, high sensitivity), but I'm betting it isn't. It could be anything, and I'd pin it on the game rather than the mouse.
they sleep on there work benches :S
