Z axis threaded rod question

[zx81]

Hello all

I'm just ordering parts to build a new 3d printer on my current printer prusa i3 Aluminium frame the Z axis uses a M5 threaded rod and nut, I was thingking of using a M8 or M10 Leadscrew and brass nut, the thread pitch on those will be 1.5 / 2mm which is greater than the m5 thread pitch on my current z axis.

so I assume my Z axis speed could be quicker (less rotations per mm) I think I will choose the 2mm pitch option should I change my stepper motor from a 1.8 deg to a 0.9 deg stepper thus keeping my original settings in my firmware or stick with the 1.8 and have a quicker z axis ?