Agree with Jonathan regards the Z axis screw 1605 is correct choice.

Regards the 1610 on X & Y then I don't agree it's the correct choice at this length. Yes it will allow slightly better acceleration than 20mm but with using servos you'll have plenty enough anyway. 20mm screws will handle whip better and give a good balance of both allowing higher speeds if needed, with 16mm higher speeds will be limited due to potential whip.!!

Both would work but given servos not steppers then really think 20mm are the best choice at this length.