Remember one of the very first wind foiling videos when Robby Naish took off on a 4.7 and a 120 liter board in 8-10 mph and we were like sweet no more big sails and barn doors..we can all do that with a foil!
Then reality set in and only a few % of people lived on Maui and even few of us were Robby, so the rest of us made a compromise on board and sail sizes.
I was gutted, pumping a 7.8 NP RS:Flight on a JP wide board, it was killing my back and I was losing some of the desire to chase light winds again, so there had to be a way of milking the light stuff while having maximum of fun on free-foiling equipment and thus my light wind and small sail size journey began.
I went from 7.8 then 7.2 then 6.4 then 5.8 and that's where I stayed for a while...now my biggest sail size is 5.0 and I'm no featherweight either at a spritely 200lbs/90kg (add a few more pounds for wetsuit and harness etc.)
I don't think I can get to 8-10 mph with a 4.7...but with some sail and board pumping the 9-13mph on a 5.0 is just enough for some summertime cruising, nothing beats flying along with barely a white cap insight, it's almost like you are bending windsurfing physics