JUST ,looking at F-race vs slalom board rocker, which would be faster in flat water ,a flatter rocker or more rocker ,
the flat in the tail area is longer in f-race boards over slalom ,but in flat water would you really notice the difference ,
does a flatter rocker create more drag ,or once planing would they both sit up out of the water and be on the tail ,and its only in
rough conditions you would appreciate the extra rocker ,how much better would a full slalom board be in speed .in perfect flat water .
or is it the width combined with rocker ,which creates the super speed .
I think there is a perfect mix for the conditions.
Flat wetted area should be faster .
Longer wet area slower, but a board will lift to the wetted area thats equal to the speed.
I hear a shorter wider wet area is faster , ( cutouts ), but speed boards are long and narrow.
A longer front rocker will increase wetted length but also slam less into chop.
I have a slalom board which is very short and wide and almost no rear rocker and not much at the front either . i suppose its built like this for good riders to adjust to the pitch of the water over rough conditions . And be able to turn . Way above my skills , And a good racers board doesn't really touch the water that much , flying on the fin in the face of danger overpowered.
I would think each board combo works different , so many variants and what you think might be faster , may not be.
So to answer your question...dunno 
there is no straight answer for your question.
while a flatter rocker is hands down faster. no board has a flat rocker. a rocker is a mix of curves and flats.
so there is no real answer other than to say in general flat is faster.
more important is change or rocker.
i don't buy the longer length slams less idea.
Tardy have a look at the older mistral board.theres three going on S.B.buy& sell.sorry l have no input on rocker design,but these boards are fast.
thanks for the answers ,why i ask this question is my fastest board i have has the flattest rocker line ,and agree what gestalt says ,
no straight answer ...I'm guessing board designers are working on it every year ..is it faster this year ? no lets change it ,will they ever hit the sweet spot ? I think they are closer than ever ...we have never been faster 
(windsurfing) but why .what has been the big change .
even though quite nasty on the ankles when rough ....my 92 patrik is still my fastest .. .I've never been faster ..yet...
its a tough question ,but i'm guessing a combination of things would make a difference ,but i'm thinking flat water only .
What skips faster with less drag - a flat stone (no rocker) or a round stone (a lot of rocker).
Don't forget the rails on the back third of the board - Sharp/hard = faster. Soft = slower
