Scuttlebutt has published more from the surprisingly informative interview with Artemis honcho Paul Cayard (scroll down to find Part 2 if you have already read Part 1), and he digs even deeper into foiling, and the tradeoffs between losing displacemnt downwind and adding drag to your boards upwind.
This is the classic sort of America's Cup discussion, which could easily involve more than a few head fakes, so it's hard to know whether to take it all as gospel. But it's still pretty interesting, in a Kremlin-ology sort of way.
Here's a taste (but read the whole thing):
With the focus on full foiling, it is important to recognize there are wind crossovers that impact the equation. If the winds are too light to fully foil, then the excessive drag caused by the foiling blades will be a big problem. While July and August are windy months on the Bay, September can offer a wider range of wind strength. The foiling package that works in the Louis Vuitton Cup (July 7 – Aug 31) may not work in the America's Cup (Sept 7-23).
So far no team has been able to fully foil upwind. We see it when reaching and running, but not closed hauled, and I don't think we will see it in this America's Cup. But remember, even if the boats are not fully foiling upwind, they are still foiling to a less degree. A good estimation is that about half of the boat's displacement is getting lifted when sailing upwind.
Meanwhile, here's Team New Zealand showing what it all means out on the water, and showing how the whole foiling thing is done, in a video shot by some non-spies (i.e, a couple of guys out for a fun day on the water). Note: the breeze was 12 knots.