I guess we should ask ourselves first why we want to buy a double even before we go into the market.
Regardless of price, I believe the vast majority of users will be because of the great workmanship that goes into these magnificent rifles that they have confidence to use them for hunting dangerous game should the chance prevail itself.
The romance of the great safari is still with us well over 150 years on; now to do so might be a pretty slim chance at present, however the skills to regulate these beasts with something besides factory loads are another challenge altogether, (I'm certainly finding that out) not for the faint of heart. It takes a lot of time & money to do so, but that is the challenge!
If we all like the same old .345 Remchester then it would be a very boring old world where ever bullet goes exactly in the same hole time & time again (sorry to the folks that love doing that sort of thing!), so hence why we buy what we do - because we want it.
Regardless of price, these are all individual & unique, did you pay too much for rifle, perhaps you did - so what! We are just the caretakers of these fine arms, they outlive us all, so why bother.
Vette447 has the right idea, buy them for posterity's sake; if they are in my care they will get used lovingly until I pass them on to the people who deserve them.
So if you are just in the market for a double as an investment only then frankly you shouldn't own one because that is not what they are truly for.