Gauging Resolution Is No Cakewalk
Resolution is a complex issue. It is measured in cpi (counts per inch). The more of these counts there are per inch, the shorter is the distance the mouse has to cross. Practically speaking, with a resolution of 800 cpi, the mouse will not need to move so much to cross the screen as it would at 400 cpi. This obviously creates a sensation of speed because if the distance is short, you will have the impression you are moving faster.
It gets more complicated as Windows and gamemakers provide the option of changing the value. By default, the average value is that of the mouse's resolution, unless the mouse maker offers sets the mouse's resolution, which trumps the default settings of Windows and the gamer makers.
In practice, it's not a case of finding the top speed but the best speed, because if you go too fast, precision will suffer. This is not due to the mouse itself but to movement, which is too fast for an accurate aim. Logically, the display resolution has a direct influence because, in 1600x1200, the distance to cross is much greater than in, say, 800x600. As long as you stay below 1280, a mouse at 400 cpi is fine in a normal position, though beyond that, especially for games, you have to speed it up via the settings. The mouse then loses precision because you have taken it beyond its physical limits. Frankly though, such loss of precision is really only obvious in 1600x1200 and, even then, not everyone would notice. At 800 cpi, you will never need to speed up the mouse because, even at 1600x1200, the default speed is pretty fast. If you raise it, you will not be able to aim at a specific point, and in fact you may even slow down, though that will do precision no harm. So 800 compared to 400 has a slight advantage in a high resolution above 1280.