Hi Mr Wind,
First thanks for your trust in your current Fanatic quiver. Yes, when the wind drops with a 5.3, the Stubby, being fairly narrow, is a bit trickier to float/ride in light winds. I would actually go for the 95L as your biggest sail is a 5.8/you are pretty light.
The older FW tends to ride higher out of the water due to the narrower tail and general rounded outline/bottom shape - so it rides up onto the fin, which makes it feel very "free", but this is not great into steep chop/overpowered. Whereas the newer STB or 2020 FW, have wider tails, lower entry rockers and the straighter outlines- so the board rides at a more practical angle to the shop, so the tail is more up/nose further down, so you feel like you are floating over the chop - instead of ploughing directly into it.
The STB is obviously a bit of an adjustment for classic FW users, who may be quite back foot oriented/but since you already have a Stubby, should be no problem to get used to at all and you should feel quite at home? Good luck!
the 2020 model is a blend of the previous FW and STB´s, in terms mainly of optic and some fin tuning on the shapes in the nose and the tail, also well worth a look if you can find a good deal, I would really recommend the newer shape too.