I've really only seen 4 causes of piston/cylinder wall scoring:
1) No/poor chamfer at bottom of cylinder bore. At bottom dead center, the piston protrudes of the the cylinder a bit and it rocks a little. If there isn't a proper chamfer there, the piston will become scored.
2) Poor cleanliness during assembly of the pistons or installation of the pistons into the engine.
3) Handling damage to piston during assembly or install.
4) Material in intake tract sucked into cylinder scoring walls. Material can also come into the cylinder from the exhaust system as well due to natural overlap of the valve timing. I have seen failed cat. converter material in cylinders before. It is very gritty and wears down the bore and rings in no time.
As far as additional boring goes, going past 0.500mm oversize poses lots of potential problems. The liner starts to get thin. The head gasket starts to overhang the combustion chamber. The existing sleeves are cast in and have ribs on their backside. They cannot be simply pulled out.
If you want to find out what 3.2L or 3.5L equals in oversize, do a little searching for the stock bore size and stroke and do the math. It is fairly simple.
