From my point of view, if you are using steppers, they should be direct drive. If you are using servos, you may or may not include a reduction ratio. When I look at typical torque / speed curve for steppers, doubling the motor speed by introducing a 2:1 reduction ratio reduces the motor torque at a given speed by the best part of 50%, so you don't end up much better off. In the meantime, you've lost half your speed.

With a servo drive, you typically have 3000rpm or so max speed with full torque available. With a direct drive and 5mm pitch, that would be an unusable rapid speed, even for bragging purposes down the pub (15000mm/min). So for a servo, a reduction (somewhere between 2 and 3) seems to make sense. A stepper couldn't pull the skin off a rice pudding at anything near those speeds.

As for stall force, unless you plan to use your machine as a press, that doesn't seem to be an issue. How much radial force can a tool take before it breaks?