I have had a 5.5 destroyer for about 5 years now. I have found it to be more than capable in the rough. My only criticism is it feels a little stern heavy with the E-tec 115 on the back. If I could spec it again I would probably settled for an E-tec 90 which is 40 kg lighter. The E-tec is right on Humbers max weight limit for the hull.
If you really want a rough weather boat, not that the destroyer isn't very capable, I'd look at an ocean pro 5.5 which will be even better.