Large Four-Person Yacht

My four characters are going to be sailing a yacht from the Northern coast of France all the way round France and Spain, through the Gibraltar Straits and across the Med to Turkey.

What I really need to know is, what is the biggest yacht the four of them could plausibly sail? And how long, roughly, would this take?

Relevant Info;

The setting is present day

All four are very experienced sailors and have sailed trips like this before (two have circumnavigated the world together)

All four are men, fit and healthy and in their twenties

They're going to be sailing in the middle of summer

They're not pressed for time, so they'll be going at a lesiurely pace

They're also going to stop in at Greece and pick up a fifth passenger, another experienced sailor


I've used search terms such as 'large four person yacht' and 'luxury yachts' and tried searching for information relating to that route.

Thanks for your help! :D