RE: 6.2 vs 6.9 planning threshold
Han, I don't know the 3S so well and it _will_ depend a lot on the particular shape. 6.9 is probably on the edge of what is effective and you will need a fin to go with it. I would guess that despite worse handling and a bit of a bogged down board, you will be able to plane a bit earlier (cant quantify in knots though).
As Steve says, smaller quivers/bigger spacing works finw with modern sails, but I don't agree it make choosing sails any easier. There will be times when one is small and the next one feels big and then choosing the wrong one will have a big impact on how much fun you will have. With more sails, choosing the wrong one will not make that much a difference.