Personally, I would never buy ones that big. They tend to get tough when they are that size. When we caught ones that big, even from deep water, we always used them for lobster salad or in some other type of dish, never just to eat on their own like Dan did. I'm 5'2" and the biggest we ever caught was end of tail at my shoulder/arm joint to nose tip at my fingertips. That one got used for a huge batch of lobster salad.
Stone crab claws are the same way. The bigger they are, the more shell weight you are paying for and the meat is not as tender. Don't ever buy jumbos or extra larges unless you are trying to impress a tourist. Larges are borderline. Mediums are your best buy.
Also, don't ever buy from a road side vendor even if they are advertising a fantastic price. The crab claws and lobster are usually good (the nose knows), but they are selling "lights" that the fisherman needed to get rid of because markets won't buy them. They are animals that are either getting ready to shed or have just shed and the meat is not at it's prime.