It's a pleasure. My CNC engraver is about 900x700mm (thats around 3x2.3ft) and the 17's work for me. Remember it's not really about size it's more about what's resisting the motor. I do understand that the bigger in size the more weight it will be for the motors to move, but as long as there is as little friction as possible, then you will be ok.

Don't let me sway you from getting NEMA 23's. I'm just giving you my perspective and what I've discovered with steppers. The more torque won't hurt, but just always check the holding torque and the amperage drawn. If you do go NEMA 23 then try to find one that will give you the most torque around 2A.