Do you have much experience in sailing? If not, work on that a while, then you will have a better idea of what will suit your style of sailing. I don't know, but my guess is that single handing a 56' boat around Cape Horn or in the Artic Sea might be a bit difficult, if not downright dangerous and overwhelming.
Also, one doesn't have to have "the ultimate" boat. It doesn't exist. But there are lots of boats that would work, although, I grant you that a tall person will need to make sure there is sufficient headroom. And for most of us, a little thing called money availability tends to narrow the list of boat possibilities.