With any regualr stepper as speed goes up torque goes down.. I am sure there is a way to gear it correctly but I dont no the formula. And even after it is geared I realy dont know if it is linear. I would fear you would loose position over long distance as the speed ramped down if it does not get into the correct torque curve of the motor, would it loose position?? I am new to steppers as all my machines are Servo so rapids are not an issue. I am just starting with my first stepper system with the new plasma table I am building.
You may want to contact a MFG of the stepper you want to use and ask them where you need to be geared to get the best of both worlds.