You design for the fastest speeds you plan on using. You can always slow down. Unless you have a very low resolution setup, movement while going slowly should still be smooth. Even with 2 turns per inch screws, if you use Geckos with 10 microsteps, you still have 4000 steps per inch. To move 2 inches per minute, the PC will send 8000 steps in 60 seconds, or 133 steps per second. So if the motor is moving 133 steps every second, it's going to be pretty smooth.