What type of "threaded rod" are you talking about? Leadscrews don't work very well at that length, unless they are very large (and very expensive) ballscrews. Most people use rack and pinion for an axis that long.
To properly choose the correct motors, you need to know how much weight you'll be moving, and how fast do you want it to move (both acceleration and top speed). Only then can you choose on what size motor you need. Also, the motors, drives and power supply all work together, and if any one is a poor match for the system, the others may not operate at their full potential.