I'm 183cm, I love my 30". I bought them by mistake once around 2008, and I hated them. My forearms almost died and I couldn't sail. The next session was better. Since then I can never go back. I used 24" when I was sailing flat water only. Then I sailed in the ocean I found big swell a problem to control. I sail 99% of the time in the waves, high boom, 30"lines. I take my freestyle board out with the same boom and lines with an old Concrete Wave fin that I cut down with a jigsaw to 16cm and I'm still plenty fast and able to go upwind. I never sail bigger than a 5.6.
But as someone said, it is indeed a personal preference. However for ocean/waves, I would say 28 or 30 or 32. Each to their own

If I sailed flat water with a big sail I'd potentially go a bit shorter, especially for long upwind runs. I've seen too many people have excessive catapults with short lines, but hell, who am I to complain. I love the show they provide