Since like forever , i've used logitech mx518 to play qw. As most users of this mouse is aware, the old logitech driver does not support increased USB-pollingrate.
In a OS that requires all drivers to be signed (vista/7 home premium), you would have to go thru a lot of hassle to sign a hacked usbport.sys with a test-signature and enable driver testing.
When this finaly succeeds, you would still be stuck at ~600-700hz pollingrate
In g400, logitech has recognized the greatness of mx518 and kept all the good features like shape and price, but included a modern driver that supports 1000hz out of the box. I did some playtesting and the only difference is slightly different color and maybe the cord is bit lighter.
A round of xs4all playtesting delivers the hard fact:
You will not automaticly win dm6 vs locktar using this mouse alone, but you will atleast slap some noobs around in the ffa proof