I was only thinking about this last week. I'm sorry to say that I have not paddled my mates full carbon Boost X LV in good downwind conditions. I've used it a couple of times in very mild conditions but not surprisingly that didn't reveal any significant differences.
Current boats
Epic V10L Ultra, Epic V9 Ultra, Fenn Bluefin, Nelo 600, 550, 520 & 510, Expedition Kayaks Azure, Mirage 732.
Previous boats
Spirit PRS, Fenn Swordfish, Fenn XT, Fenn Swordfish S, Think Zen, Epic V10L Club, Carbonology Sport Boost LV, Carbonology Sport Boost X LV, Fenn XT double.