i have a 12m and a 14m because i share them with my bro who is a little lighter than me ,i am 94kg . the gap is good for us in that when we are both out he can use the 12m and i can ride the 14m .
but if it was just for me i would have got a 15m the gap between a 12m and 14m is a little small . But it is very important to think about the board size and the wind conditions where you live . you can hold down a bigger kite with a smaller board and you can get going with a smaller kite with a bigger board .
anyway some thing to think about.