Is it better to have a higher reduction gearbox and have a bigger pinion on the rack or less reduction smaller pinion?
The gear drives would be Alpha SP planetary 35:1 with 4,000 RPM servos if this is the way to go.

Or does it depend of a lot of other things?

Thanks

If you go with too small of a pinion you will not have enough teeth in contact with the rack. This will cause a condition called jumping when reversing or sudden starts and stops. I know that there is some engineering data out there that calculates the min. number of teeth in contact based on the gears pitch.