I had been working on the assumption that a faster pitch is best for a CNC router because that is what I read here before buying my screws but I just read that a corse pitch reduces the "resolution". Is this correct?

If it is, to what extent does it matter on a diy benchtop CNC machine controlled with steppers and a Gecko G540? i.e. Can you even notice the difference in "resolution" between machines with 5mm pitch screws and ones with 20mm pitch screws with such a set-up?

I will only have approx 31" x 16" x 8" of travel / work space. If I upgrade the ball screws on my build, is it better to look for a corse or a fine pitch? There seems to be some good deals around on ground C5 ball screws with a 20mm pitch but, should I be looking for a finer pitch instead?

Does the grade of ball screw matter when choosing the pitch? I.e. Are the gains in "resolution" on a 5mm pitch screw negated by the loss of accuracy from choosing C7 grade instead of C5 or C3?

Does it matter what you are cutting when selecting the pitch size / speed? If I will be cutting aluminum, do you need a slower pitch than you would for machines that cut softer materials?