The only reason I ever had O/U barrels backbored was for weight reduction. Taking out .012-.014" removed nearly 5 ounces from a 32" set. The $400 at the time was worthwhile on a $3K clays gun. The people who do that kind of work are certainly capable but, at $200 per ounce I don't think I'd consider it on a SxS. I suppose you'd get chokes of your choice included in the cost, but I'd still consider another gun.