With that large a motor you could easily use 4 or 5 TPI. That multiples the torque by the length of the thread over one inch (not just the TPI number). The larger the dia the longer the thread. You can go higher in TPI but at 10TPI you need a higher pulse rate from MACH so if you want the IPM on Z to be 120 IPM you need 200*10*10*2 or 40,000 pps (pulses per second). Pretty high. 5TPI puts that same rate at 20,000 pps.
Since the max velocity for the THC is limited (THC Rate in MACH3 uses a percentage of the max velocity since acceleration curves are NOT used under THC control). you will be running the axis at 20 to 40% of the max velocity. That means if you can do 120 IPM with accel you will be at about 40 IPM. That means that if you are moving XY at about 3.3 IPS the Z will only move about 1.1 IPS. The max up angle then is slighlty more than 30 deg (1.1 inch in 3.3) rise. As long as you aren't trying to cut wavey sheet steel (siding) at fast feedrates then a 30 deg rise rate is good.
The tradeoff to faster speeds is lower resolution and that can effect the accuracy of the THC moves. If the smallest step you can do is .010 then the moves can get pretty saw toothed as the tip volts bounce back and forth.
Yep, 4 ot 5 TPI is the answer!
Tom Caudle
www.CandCNC.com