Firstly I know little to nothing regarding routers but what I do know is that you will struggle to cut steel with any precision
on a 4 x 3' table. Rigid routers have small movements and are massive to gain rigidity. You may be ok with aluminium but
subject to the precision / tolerances required may be up against it!. Ballscrews are more accurate generally and don't tend
to wear 'loose' as quickly as lead screws. Nothing wrong with a toothed belt drive if tensioned correctly every movement will
be transmitted - any joints in the driveline is where the slop and backlash creep in, messing everything up.