I'm building a cnc for wood and aluminium.

I have a 1000mm y axis ballscrew, 1605
Also, 700mm x axis 1605. (Haven't purchased yet, 2005 maybe?)
Z axis will probably be 250mm ballscrew.

I'm looking at my z axis. It has the 2.2kw water cooled spindle.

I was automatically going to get a 1605 for z axis but, smaller would be easier on the build and am I right in thinking the 4mm pitch would be more accurate, but slightly slower?

Any real disadvantage of using 12mm ballscrew on Z axis? Cost isn't a big factor, just wouldn't mind a slightly smaller assembly.

Am I better with 4mm pitch over 5mm? Accuracy preferred over speed.

Thanks.