rough outline of what we do at work. prime, block with 180grit dry paper, dizzy with 400, if solid colour (white,red ect) super fine sanding pad edges hard to get places, if metallic wet rub with 800 and 1500 for blends. this is for 2 pac but never had an issue yet, just need to be sure to get all the scratches out. also for guide coat we use a purple dye guide coat as it is more even and easier to block with, sometimes use a black gun generally on bars and such when we just dizzy them.
also i fail to see where 320 dry would be the same as 600 wet.. 320 is far courser than 600 and wet rubbing is less harsh than dry rubbing.