The bigger the motors, the slower their maximum speed tends to be. You're screws are basically 5 turns/inch, so you need 500 rpm to go 100 ipm.
Depending on inductance, most steppers have a maximum usable rpm of about 1000. Although smaller, low inductance motors can be good for up to 1500rpm, or even higher.
I've seen torque curves of similar size motors that only have 150-200 oz-in of torque over 300rpm.
You'd be a lot better off with screws with a 10mm lead, or even 25mm lead. Those would give you 2 or 5 times more speed, while keeping the steppers moving slower where they have more torque.
Your 5mm lead gives you a large mechanical advantage at the expense of speed. At very slow speeds, you're probably getting several hundred pounds of force. But at high speeds, you have none.
Going from 72V to 80V probably wouldn't make a noticeable difference. And likewise, while changing motors would give you better performance, those screws are still hampering your performance.
To answer your question, big motors and 5mm pitch screws are best used on big, heavy machines that need lots of force, but not higher speeds.