RE: Apollo Vs F161
Yes, the FW class rules set a wind limits at 6 knots and yes, a FW board can plane as of 6 knots with a big sail (11-12.5 sqm), depending on your weight and skills (plenty of posts on this subject).
Althought both the Apollo and Serenity target ultra light wind, they do on different scale with distinct segment's end results : planing with the Apollo as of 4 knots (true ?) or "gliding" with the Serenity as of 1-2 knots of wind.
The Apollo looks extremely interesting to me because if I can achieve planing as of 4 knots with that gear, this will be a very significant leap from my actual 7 knots of wind planing threshold with current gear. I mean 4-6 knots of wind is 2 Bft, i.e., almost half the wind force of 3 Bft (7-10 knots). By contrast, FW's planing threshold is only 6 knots, so not worth the investment just to gain 1 knot over 7 for my case...