Stepper motors should be chosen by looking at graphs showing torque against speed. You can mix and match. They are all 200 steps/rev which suits 2.3" a lot more than it suits 3.4". The stepper market is dedicated to American's who believe more is better and need to be told what to do and what to buy because that is how they were taught in school. Why do you want to power the bed vertically when you can power the quill? You can put a screw along side it. Fix that backlash first or it haunt you.