There was an excellent previous thread on the theory of regulation of doubles here and I believe the gist is that when regulated properly the barrels of a fine SxS shoot consistently parallel side by side out at extended ranges where as the O/U would shoot high/low.

If the Doubles barrel angle/regulation converges then the paths could be made to cross in a shorter distance and diverge further out.Hopefully proper regulation could benefit this situation.

True the recoil of SxS barrels goes outward but this is controlled by the resistance of the shooter and should not affect the bullet path if the recoil is "contained".I would agree that theoretically the upward/backward recoil of a O/U would be more conducive to accuracy at extended ranges than the SxS.

With proper regulation a quality Double can shoot out to 250+yds and one forum member here has taken game at 300yds with his scoped Double.

I hope this is correct as I would love to shoot a 375H&H Double out to 250+ with a qd scope. That would be NEAT!!