I don't know the actual volumes of the Kode 86 nor the 94. But I have sailed it and to me it feels very "86:ish", for sure not anywhere as low as 80 liters. In any case, the 86 is the right size for you when you only weight 65 and will not use a sail bigger than 5.9. It will plane just as early as the 94 and the only positive side of the 94 for you would be more stability when not planing and better performance with really large sails. But that will come at a rather substantial price in terms of much less overall range and a much "clumsier" feel once planing. So, even as a "big board" (up to 6.3) the 86 will be a much better fit and I think it will give you the feel you are missing in your 97.
I'm just over 70kg myself and wouldn't want a bigger fsw board. I've used the Kode 86 up to 6.3 which works great (with a slightly bigger fin than original).