I think Rocketman offered some sage advice, and you may be planning on it anyway, but go to London and spend some time with various makers.

A good friend of mine who owns all the names being discussed went to London to commission a 20 bore Purdey. He ended up with a Watson Bros. and it is a marvelous weapon. The rest of his guns all had previous owners. I have handled all of these, shot some, and for me I liked a 12 bore pre-war Boss he owns.

All the best, and I don't see how you possibly go wrong with any of them.

Chicago Mike