Hi Dingbat. Welcome to the Zone!
If you already HAVE the 4 HobbyCNC 425s, they are 57V motors. They will give you very fast rapids wired Bipolar Parallel with the $299 50V 3.5A G540 and a $129 Keling KL5010 PSU. They are 4.2A motors when wired BP, so there will be a slight loss of torque when run at 3.5A--But they still should be plenty powerful enough.