I have the king , a 6’ kite surf board and a home made sectorish raceboard.
Surfboard and king work in roughly the same wind conditions with the king being the goto unless the waves are really clean.
Race board is now in its 3rd generation and uses tuttle boxes and wind surfer fins.
Things I have found.
1 fin position is critical. You drive off the fin so your fins must be inline with the centre of thrust from your feet.
2 foot position is a pain . To far forward the nose won’t ride chop. To far back the board drags. To far out it is difficult to carve on to toeside for the gybe and hell to do waterstarts because the board stays on its edge and carves straight up wind. To far in and you tend to put the board on is edge which ruins the effect of the fins This and above is why I am on the 3rd board.
3 Nose lift You need more than you think. a normal board you use the edge so it will cut through waves . A race board is run flat so the nose has to get over waves.
4 Deck needs to be rounded so you feet are at a nice angle when riding. Flat decks and boards flat on the water make painful ankles .
In the light I use 2 x 1’6” Mr Dice and Mr Slice The advantage with tuttle boxes or the similar is fins are readily available
I have tried 2 and multiple fin layouts and have found 3 or 4/ fins gives good tracking but are a pain to turn. 2 big buggers goes up wind nearly as well but can also be carved for small waves.
With a 14m Razor as soon as the kite will fly. by 10 to 12 mph a smaller kite is needed.
Construction need to be strong with a ply stringer. there is no point having a fun board if you are fearful of getting airborne.
The Sector shape is good for early plaining and fun whilst still retaining upwind performance but will never be a true race board the. North race board leaves it for dead but the North is uncomfortable and is only for those who want full on racing.
The main problem with all of the “race” style is cost. An effective solution is to buy old windsurfers cut the end of fit a couple of fin boxes ( One robed from the old board) move the toe straps forward and away you go foe less than £150