This is not the same answer for everyone.
Depends on kiting or sailing experience, commitment to train regularly, if your typically fast or slow at picking up new sports etc.
If you have no kiting experience I would recommend a sector style board or twin tip and two or three kites, this will get you going for the first 6 months or so in most wind conditions and the boards will have reasonable resale.
If you allready know how to kite and are committed to putting in some serious training then get at least a 2012 700 wide board with good fins, after 2 or 3 months you will want to be hitting the course, getting any less capable board is just slowing down your progress towards what you want to achieve.
If you are a slow learner and or cant get much time to practice get a sector or twin tip and progress from there.
After it is all said and done there is only one option atm to win around a course.
That is a 2012 70cm wide 3 fin board
Fins from one of the specialist fin makers at around 42 to 44 for front and about 38 to 41 for the center
And race orientated kites.
If anyone is winning on any other board then the other racers they are up against are not yet up to speed

PS: I have a 2012 north board for sale, same as what Florien won sail Melbourne on