I recommend 500 Hz, in mx 510/518 u have stable rate, when u have 1000 Hz rate is chengenable. Imo for mx 510/518 - 500 Hz, for Razer diamondblack - 1000 Hz. New mouse like logitech g5 (500 Hz) and razer cooperhead (1000 Hz) dont need usb patch because them driver use high usb rate in default setting.

Just be careful with this stuff cuz u may damage your usb ports and also keep in mind that the higher u set the polling rate, the heavier the burden becomes on your cpu - important especially now with q4 coming out - so maybe not really worth setting it really high. I dont think there will be any noticeable improvement from 250Mhz.