I have built them both ways on factory actions, no differences in accuracy which could be directly attributed to shouldered/non-shouldered barrel.
Its really about aesthetics, IMO.

If you want the smith to do a shouldered barrel from a blank, you really should go full monty (or just stick with a quality spin-on prefit).
True the the receiver face, true/cut receiver threads ten thou over, cut the new barrel tenon to fit- just as you would with an M700 action.

You're not going to realize any accuracy gains from a shouldered barrel for the extra cost incurred unless you go the extra yards. Once you go that route though, you'll always need a custom barrel.

If you like the aesthetics of the shouldered barrel, you can still change it out- just use the witness marks on the barrel and receiver. You'll need an action wrench and barrel vise instead of just the vise and nut wrench.