I assume that your steppers a direct coupled to the lead screws? You would be better to overdrive the lead screws by 2X and slow the motor down using a timing belt drive. The would allow you to operate the motors at a higher torque range. If your gantry is only 200 lbs, you might be able to overdrive by 3X given the torque of your motor.

Here are the specs on my machine for comparison. I have a 4x8 moving table machine, but the principal is the same.

Stepper motor 1280 oz/in, 6.3 amp, 80V power supply
Table weight ~700 lbs
Lead screw 40mm x 40 mm pitch
Drive ratio 1.5:1
Table movement / motor rotation 26.6 mm (1.049 inch)
Microstepping set to 100x
Absolute max rapid speed 600 IPM, normal rapid during operation 500 IPM.
Motor RPM at max rapid ~560 RPM

To reach 600 IPM the acceleration has to be set a bit low, but at 500 IPM normal acceleration works fine. At 60 volts and your motors you may have to live with slightly lower acceleration and a little less top end.

I hope this helps