There's one step before yours: measure the bores first, determine the dimensions of the worst one, then figure out what size pistons you need to clean up the hole.
I'm rebuilding a small block Chevy right now. I measured the worst hole at about .017 wear. I thought about going .020 oversize, but the machinist talked me into going .030. He said I likely could not measure the full extent of the wear using a rounded tool up against the ring ridge step. Made sense to me.