Barney: It depends on what type of sailing you will be doing. As long as it's not wave sailing you can get away with a bigger board and if you want to do freestyle it can be an advantage. The Kode 80 has a narrower tail and will maybe not be as easy to pop jumps one. But on the other hands, people do radical freestyle stuff on wave boards all the time, so its not like the 80 would not work.
If you're primarily interested in freestyle you could also go for one of the smaller Flares which are in fact also very nice boards to just ride around on.
But as far as Kodes go the summary for you would be
Freestyle priority => Kode 86
Best "fit" and widest range overall => kode 80