Greg,
I suspect that our use of a gun, here in the states, does not always dovetail so neatly with what has been termed as "Best" in English guns. We tend to be, here in the states, what the English would call "rough shooters", hunting all day, with many miles of walking, for occasional birds put up over flushing or pointing dogs. It would not be unusual to take a spill with an uncased gun for us. A British best gun was developed for a pretty narrow shooting focus, that being driven birds over a peg, typically. You walk to the peg, with the gun cased, by the way, shoot from your peg assigment, case your gun, and walk back.
My point is, you may need to reconcile your own use of a gun (you plan on using it, right?) against what is typical in features of a British Best gun. Pheasants driven straight at you are a hell of a lot easier to kill than the same birds fleeing straight away, and a gun set up originally for a 1 1/4 oz load might be more suited to your
use. Those in-proof at .021 thickness barrels sure swing nice, but, they don't take all that well to a fall after you trip over a hidden barbed wire fence, or the dog knocking them down as the gun is resting against a tree as you relieve yourself.
It's one thing to say you have a Best gun, it is surprisingly different to have a gun best suited for your use of it. Give the whole idea a bit of thought, and take others opinions of what constitutes "Best" with a grain of salt-they aren't paying for it.
Best,
Ted