If u have an accelfix installed, use Operating System.

... or use 'Setpoint' and make sure that your Setpoint acceleration is set at zero, which should have the same effect.

yes although logitech never explained what setpoint implementation even does, besides overriding windows acceleration . It really has a different feeling (added lag/filtering/smoothing). But someone has to be very sensitive to this kind of stuff to notice. Afterall OS inplementation should give a more driverless feel.