Large gantry style router, Do i need gearboxes?

Hi Folks! 

I'm planning my first large gantry style router machine (table ~2x4.5m  Z ~250mm ) , which would be used mainly for plasma cutting, but also for milling wood / aluminum and plastic.

On X and Y axis, I would like to use rack n pinion system and my question is that, if I use Nema 34  ~10Nm steppers is it possible drive these with direct drive, without gearbox? I would put smallest (diameter) heavy duty gears i can find. My concern is that is it going to be too fast? Does it still need reduction gearbox? 

Second, if i can afford it, is the ball screw always better option on Z axis, or is there reason why I should select leadscrew on that? (less backlash etc? no need for braking?)

  www.t2cnc.hu/downloads/Lichuan/2%20Phase...otor%20Datasheet.pdf
LC86H2128

Thanks, i appreciate your comments! 

Plasma requires a light gantry while routers need a heavy and stiff one, so having both on one machine is never a good idea, but it can work for sure with some limitations.
With rack and pinion reductions are mandatory, not negotiable, the smallest pinion is something like 30mm in diameter so that results in over 100mm of move for one revolution of the motor hence the resolution goes out the window.

Thanks for clear answers... I'm quite space constrained and that's why i was considering combo machine. I have to think about this little bit more...

Cheers!