center fin is typically 6-7", depending on the size of the rider, the wave, & preferences. at around 200lbs, i prefer a 6.5".
the extreme (15-20) cant of the 4 side fins allows the board to hold really, really well in steep faced waves, which is why a lot of people seem to like them for barrel riding boards (not to mention that they're super fast, so getting swallowed up isn't as likely), & they go rail to rail quite easily...provided you know how to use your rail, & don't just try to pivot on the fin cluster.

here's an old(er) video of mikala & daniel jones surfing bonzers in hawaii:
http://youtu.be/2H2RSCf6sNM