I have a 2004 starboard carve 90ltr with us fin box, run a 28cm fin and weigh 90+kg. Have pushed the limits to the extent that it now has a crack somewhere and is sucking in a little water.
Thinking about putting in a stronger finbox either power or tuttle.
My question is, has anyone done this and the pros and cons for either option ?

boardlady.com/jppowerbox.htm

I would go tuttle Have done the upgrade on a old Speed Slalom, But ultimately your fin quiver should be the deciding factor!(I Have tuttle in all my boards)
If you have a heap of power box fins the would be a better choice.

http://www.surfsailaustralia.com.au/showProduct/Windsurfing/Bits+and+Pieces/c305/Chinook+Tuttle+Fin+Box