The simplest and best option might be the ClearPath product line https://www.teknic.com/products/clea...sShowPopUp_100 One of the advantages is that they have the drive built into the motor, just supply power and a step & direction signal.
I have used their NEMA 34 replacement motors on a larger machine than you are working with and rapid at over 1000 IPM with no problems. They may have a NEMA 23 that would be a drop in replacement for your current motors. Your existing motors have a torque curve that drops off rapidly with increasing RPM, where the ClearPath units have a nearly flat torque curve up to their rated RPM.