RE: Fin for F160 non racer
Why not the one that comes with the board? When I tried it a few times I think it worked pretty well with my 11 Vapor and 95kg, as long as was not trying to plane in too little wind or going for max angle in +20 knots or otherwise playing with the boundaries of it's range.
That said at 90kg and from 7-14knots getting a good low-end fin like the Deb R19S-- +8 might make sense; at 90kg you should have no problems up until 14 knots. I'm currently waiting for one of these for my 160; but plan on using it with a 12 Vapor in less than 12-14knots only. Alternatively (probably the better choice) the R13S +8 is a very very good allround fin for the F160; especially if you do not really need the last degree of height at very low winds, and this fin will not not be overpowered before the sail for sure.
In your shoes I'd use the std. fin (if you have it?) or alternatively consider getting the R13S+8 which is a really good quiver-of-one fin.