Deciding to gear down your steppers is a balance between rapid speeds and torque available while cutting. Most systems use steppers direct driving the spindle due to their limited rpm range and declining torque/speed curve.
For say an upper end of 1000 rpm on your motors, thats going to be a rapid speed of 5000 mm/min, or about 200 in/min. Thats pretty quick for a small table.
To figure force you can use the equation given by figure 11 at the Nook site here:
Ball Screws, Ball Screw Glossary
This equation will give you the linear force applied for the load you will have on the table. Run your numbers through this equation and see if you think you will have sufficient force direct.
If you decide to gear down your steppers, the torque multiplication effect will give you more cutting force at the expense of rapid speed.