Hi Simon,
Well, of late I have been avoiding the less-good days, and I am using a pair of 5’4" Romanoskys, one quad and one tri. I run about 1.75 m tall and around 80 kg. With the UDTs and glassed on fins I am mostly happy with them, and on short if steep sections, say 1 m and higher faces, I can get away with it pretty well on a board that size. Plus they work well in more lined-up waves. More dimensions ( in US units, sorry) here
Now, I said ‘mostly happy’ with the 5’4"s - one thing that I am not that happy with and something that you might want to think about is floatation. At around 6 cm or more thick, I think they float too well, and I have to either paddle around or do the surfboard-type duck dives when caught inside by a set or a peak in a funny place. I would be perfectly happy with, let’s say, 4 cm thick, no more than 5.
You may want to go with a thin board, as those short-period, steep North Sea waves won’t give you a lot of time to duck dive, instead you may find it a lot easier to just power with your fins and push down under, submarining the board under power instead of wrestling it as the surfboard guys do.
Much like Carl Olsen has been describing in http://www.swaylocks.com/forum/gforum.cgi?post=256971; - I found that on thin boards I could push down on the nose, holding onto the rails, dive the board and flatten my head and body close to the deck and then lever off my elbows to bring the nose back up as the wave went past to come back up, kicking hard all the way through. It’s really a paipo technique, but it adapts well to a thin kneeboard.
You do wind up doing late drops as a consequence, staying where it’s steep and fast rather than working out on the flat, but …heh…I don’t count that as a drawback at all. For me, that’s a positive rather than a negative.
Anyhow- some things to think about -
hope that’s of use
doc…