The 4 year time frame you are looking for is going to be tough with just a 10% over since there is about 5%+ of value of forks on those coins and the value of the collectable itself.
The Fork-value is closer to around 2.5% of the Bitcoin value. But since collectibles have to be physically delivered, I doubt this is what OP is looking for.
There isn’t any reason why a collectible coin needs to be delivered if the buyer only wants the private key associated with the collectible coin. A buyer could buy ownership of a collectible coin, and instead of having the seller ship the coin, the buyer could instruct the seller to peal the coin and disclose the private key.
With that being said, I am still very suspicious of the OPs motivations.