You put your price point at an upper limit of $6,000.
That gives you the ability to buy a very fine English boxlock ejector with original steel barrels of whatever length you can find. It will be a better gun than any Spanish gun in both material quality and workmanship.
Buy the right gun. don't worry about resale now - that will take care of itself. You are not doing this to make a profit - if you buy the right gun, you won't want to sell it anyway.
Sure I have a bias. It is based on my experience - no different to anyone else here. My experience is that I have never compared a Spanish gun to an English one without the Spanish one being objectively inferior. Perhaps the fact that I handle English guns all day every day makes me more sensitive to quality. If that is bias - I am indeed biased. My advise, which is all I am giving, bias included, still stands. You don't have to take it
