A little more information:
Encoders are 2000 counts/rev
4:1 Gear reduction on the servos
Ball screw is 5mm/rev
That makes the whole system 40,640 counts/inch
Resolution of .0000246" per count. Not bad.
Big thanks to Roberto at Dyna Mechtronics for his help in all this, he's been feeding me info (what info he can give out) when I ask for it and it's been a huge help!