I have a friend who is very disappointed with the 540 XS (which is infact 5.6m) that he bought at the end of the summer. He had a 90hp Optimax which is the recommended maximum but the performances were not up to expectations. He's taking it back to have it replaced by a 550 with 115 Opti in the hope that it'll be a more satisfying ride.
For info, he wanted to use it for spearfishing in the rough stuff at the point of Brittany.
You can see it here under "Kornog" on the Brenderup trailer