Re: What is the maximum size of a boat could 2 people handle?
When you say 'sail', are you truly meaning a sail boat or are you using the general term sail as in operating a vessel?
With 2 people in a motorized vessel, I would think 65-70' would be pushing the boundries of safe operation. Although it only takes 1 person to actually pilot a boat, it's the slow speed operation, docking, attending lines, etc which require an additional person. I know I operate a 40' solo, but when docking, I have to move quickly from the flybridge to the deck before wind/current decide to move me about.
I'm sorry I can't give you an answer on wind powered vessels. Don't know anything about them, except they look like too much work for me!