for the gpm comand line add a "-r" option followed by a number, eg
/usr/sbin/gpm -m /dev/mouse -t ps2 -r 100
note that if its set too high your mouse wont move, personally i couldnt get it to work over 100
if that's still not enough add an "-a" option followed by a value(say 50)
-r sets the speed, -a sets acceleration.