The settings that you will use for your 3.0 amp driver to properly power and turn your 425 oz-in stepper motor will cheifly depend on your application and the mechanical parts you are using on your machine. In all circumstances, the amp setting for the stepper motor (according to the datasheet) should be 2.8 amps. Use the closest setting on the driver without going over.
Here is a good rule of thumb for the microstepping which will correspond to the resolution, but wil also affect torque. You always want to try to achieve the best torque and resolution for the axis you are moving but go with the lowest microstepping possible. In cases where there is mechanical advantage, like a lead screw scenario, where for each motor revolution, the axis move a very small amount, you will want a very low microstep value. This is because the mechanical configuration will provide most of the finer resolution and you will not need the microstepping to assist in this. Increase the microstepping only in conditions where the axis is not moving smooth enough, or where there is a mechanical disadvantage. A mechanical disadvantage would be where the stepper motor is causing a great amount of movement in the axis and the resolutions suffers from this condition. Increase the microstep value up to your desired resolution, but don't go over since the torque of the motor will decrease.
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I'm building my own machine using your motors and drivers. What is the best dip switch settings for the 3.0 amp drivers powering the 425 oz motors