The Kode 80 will for sure feel smaller and quicker turning than your old 90 liter board so ti will in that sense deliver what your after. If handles 5.7 well at your weight, but will probably feel a fair bit smaller carrying such a sail. If you predominatly sail powered up 5.7 it will not be a problem, but with underpowered 5.7 you will surely feel you have less board under your feet. It's far from undoable, but worth thinking about before taking the leap. At the other end, the Kode 80 handles 4.2 in a B&J situation well but in wave riding, I would like to be on something smaller in those winds. As you suspect, I think the Kode 80 will indeed feel rather close to the powersurf, despite probably being a bit wider. In high winds, my experience is that the extra with actually do not hurt as much since you at the same time loose a lot of length and that the shorter board will be less blown around. I wouldn't prefer to use the K80 in overpowered 3.2 though, so maybe the powersurf is indeed a high wind wonder.
Complementing with a Kode 68 would make the quiver perfect and give a nice overlap in the mid winds. The 68 works well already with powered up 5.0 so this will allow you to tune the feel you want in the important mid register by changing boards.
An alternative for "safer" and more relaxed light wind 5.7 sailing would be a Kode 86. You'll loose a bit of high wind capability and overlap though. The Kode 86 works with underpowered 4.7 but may start to feel to hectic at powered up 4.7.
Wood or Wood Carbon? I've had good luck with my wood carbon boards, but for ultimate strength wood is a safer bet. It is a tradeoff since the woodcarbon does indeed feel a bit nicer, particularly with bigger sails. In the 86 sie the difference is smaller though (due to the wood construction on the 86 being lighter from the start).