By my calculations, if you run mach3 at a 45kHz kernel speed and use the G540 (1/10 micro stepping) with a 10tpi screw, you can get 135ipm max. If you run a 1/2-10 5 start, so a 2tpi screw, you can get 675ipm. With the 10tpi screw, you have lots of force to move things around and very fine resolution. With the 2tpi screw you have roughly 1/5 the force (actually more than that because the 2tpi screw has an efficiency of about 77% versus 43% for the 10tpi in the same conditions) and 1/5 the resolution, but these levels are typically still okay for a wood router consider the medium you're working with. With the 2tpi setup you also might need to evaluate if you have enough torque from the motor to accelerate your load to that max speed before you reach the end of your travel. I don't have personal experience with that bit of the equation yet.