If you really have a quality grade Hussey in the condition you describe, and were the Purdey in exactly the same condition, then, frankly, you are just trading for a percieved name up grade. You certainly won't have gained 8k in actual increased quality of the gun. I have a Lang and Hussey sidelock that is a best gun in every sense of the word. Just doen't have "Purdey" on the rib. Since the Purdey seems actually to be in lesser condition, I don't believe that I would trade him even for it.