There's some following this:

are 12m's the average kite for victoria ? heading over tommorrow and unsure wether to pack the 10.5 and 13.5 or just the 13.5

A 10m bow kite is the sweet spot for Melbourne sea breezes ... which we have not had much of this season.

I get about equal use of my 10 and 13. I use the 13 a little more and on a lot of those days I should probably be on the 10. There are some days when I would not be kiting at all if I did not have the 13 and a big board.

12m is what most people have and is ok for the vast majority of conditions.