I live in south France, I am 70 kg for 1.75m, I have the quad IQ 77 2011 and the quad 66 2010 and my sails quiver is from 3.7 to 5.5.
In your case, for one board, I will go to the 74l and for 2 boards with the 77 and the 69.
The 77 is quite big and you will get enough volume in light wind and still confortable in strong wind. This 77 can be also uses as a one board quiver if you sail mainly in 4.7, but as you say you are efficient with smaller board, you can go with the 74 !
The 82 is more for 80kg riders.
I have sailed about 30 times already with my 77 and it's a amazing board.
Hope it will help !