I really don't know what kind of problems with the 07 series poster 2 is talking about as have the K87 07 and it was one of the nicest riding boards I've come across. Great crossover capabilities and a fantastic way of holding a line in a dedicated carve (both on a wave and in a jibe).
But anyway the questions:
1. My experience is the all 06, 07 and 08 are earlier planers than the 05 Kombats if you compare size for size. Maybe the K86 was just too small for the conditions where you compared it with the 105? With sails up to 6.2 and at your weight, a K96 (or K97 07) should be noticeable quicker off the mark than the 05 K105.
A thing to note is that the Kombats, especially those up to 07, have a kind of short rocker which means they will get going earlier if you get back and use and active riding style. This is where you "pay" a bit for having a rally performance oriented rocker line (as opposed to an "easy riding" oriented rocker). In other words, to utilize the super early planing qualities of the Kombat, you need to work a bit. The 08 version is supposed to have a slightly lower entry which should make it a little less technique craving to milk that last bit of early planing power from the board. But I only used the 08 K79 myself, so I can not say for sure.
Anyway you cut it, 15 knots, 6.2 and 85 kilos is not going to be easy on any board, but I think your chances should be as good on a K96 as on any comparable board.
2. The Kombat have the exact same rocker as the Pre Acids, so no, you don't ned to slow down if you don't want to. Its a fast rocker, but it is a wave rocker.
3. I would say the smallest Futura is easier to plane super early on than the comparable size Kombat. But with just a bit of practice, the Kombat is incredibly effective in light wind and when waves and stuff comes into the picture, the Kombat is definitely the right choice.