Since you've fitted a servo, it may be worth considering the bit extra effort and fitting a toothed belt, as that opens up the possibility of rigid tapping.

I wouldn't worry too much about reducing Z travel by fitting a longer motor, as the bigger problem is usually lack of Z height. My old Novamill, the Coventry EasyChange holder would just about hit the table before it ran out of travel. Certainly with a tool holder in, it would hit the table. If had kept it, I would of fitted a column raising block.