1-3 for polishing and waxing is fine and 4-6 for correction work but it depends how bad the marks are. can you feel them with your finger nail?if you wont remove with the g220 as its not up to that sort of work.you may need a rotory or even wet sanding.

if you are in doubt why not contact meguairs direct in the uk and see what they say.bernadette is really helpful