David Charlesworth's DVD on shooting boards shows how to use paper shims ( postit notes ) on the shooting board surface reference point to set the squareness of cut. Your #5 can be off by 8 thou and still shoot great using his method.

That being said, it these are new quality planes they should not have 8 thou out of flat soles. That shows no quality control. IMO, I'd return them for a swap out and insist that the supplier check them before they sent the replacements. That's just good customer relations sense. Shipping is expensive for heavy planes.