I just upgraded my router to a 12 start thread 2" pitch and it works great with a heap more speed at the router. I use Vexta 5 phase drives and with the 1/2 stepping mode, it gives you 1000 ppr on the motor and geared down 3:1 has plenty of power and resolution for what I need. I had a 2 start lead screw but it was way too slow and I didn't need the power it provided so I used the 12 start.
I would recommend any start lead screw from 2 starts and up for your router. More starts = more speed (but less power) 4 starts and 1" pitch (or greater) would be a good place to start. Just remember to gear down your motor to about 3:1 for the extra power/torque.
Steppers have plenty of power at low revs and lose power at higher speeds so it seemed logical to me to reduce the speed and increase the resolution (1000 ppr) of the motor. I get roughly 300 mm sec out of it that is usable but it is a bit scary so I slow it down just a tad.
Rich.
Are we long lost brothers. With a name like Pin Head you complement my Mononeuron. We would fit like 2 peas in a pod :-)
I am not completely useless.......I can always serve as a BAD example.