originally had a pavel bonzer made with a glassed-on center fin and recently had a box put in. i'm in the market for the center fin and leaning toward the true ames bonzer fins, but stuck on the size. do i go with the 6", 6.5" or 7". it's a 6'3 beaknose bonzer with subtle channels and concaves. i am 6 ft and 155 lbs.