I think these discussions are highly location specific and one big factor is max gust strength. Everybody has a different definition for light wind, and air density, water temperature, elevation, etc... alll play a factor. Luckily, where I live and sail, it's either windy or it's not... we don't have steady light wind in most spots... other people in other spots have different conditions. Personally, I find light wind winging to be really fun.
Have a few days on the Skybrid 5'6" 70l.... I think it's my daily driver and will replace the Sky Style 4'9" 65l. Someone asked me the other day if going to a midlength allows you to ride with less volume, and I thought it was the opposite. My midlenth boards let me ride with more volume without any penalty. I have the AFS Blackbird 6'2" x 21" @ 90l as well. My wife tried the Skybrid 5'6" the other day (she's a decent foiler can jibe, switch feet, ride swell) and she thought the extra length made it a very forgiving experience. she didn't have to set up in exactly the right spot to get going or to stand up. She always comments that the Fanatic/Duotone pads are her favorite which mirrors my experience.
I've ridden it so far with my Unit 3.0 and Unit D/LAB 3.5 with Silk 850 foil. Easy starts, and feels really balanced while flying. Feels awesome on the boat wakes, riding swell, and pumping despite being longer and a tiny bit heavier than my Sky Style 4'9". I think it's about 5" longer in front of the front foot and 4" longer in the tail.
Interestingly, this board feels narrower when setting up than my Blackbird 6'2" which is about the same width. I think the BB has that nice sunken deck, so it really settles into the water when kneeling, but both are easy to setup and get going.
I'm ~85kg right now, so the BB is near neutral and the Skybrid is -15.
foggy day clip of the 5'6"
www.instagram.com/p/C9z9gzNPx2n/