Apparently the skirt coating lets you run tighter bore clearances with the 2618 alloy, which usually rattles around. Cuts down on noise and skirt wear. Crown coatings not many bother with.
Cheers guys, still undecided. I read an article once (which I now can't find) where the guy took a blow torch to the crown of a coated & uncoated piston. Not very scientific but from memory the coated one lasted significantly longer. This was what had me thinking.