RE: Putting an NP Excess 6.9 on a Kombat 97?
In my opinion, it makes little sense to push too much sail size for a given board. Usually one ends up loosing in balance what he achieved in power, and no earlier plaining is attained.
That said, IMvvvHO this issue is somewhat related to boom length. I remember a slalom board of mine that was simply perfect with a 6.0 and did not want to behave with a 6.5. When I changed sails, and got a 6.5 with a boom length similar to that of the older 6.0, then the board was really OK with that new sail. I guess boom length (not considering clew indented sails here) can be considered as a rough guide of how far back the center of pressure is related to mast foot position. If you second this, you will prefer the Excess over the Expression due to its shorter boom; X-Ply construction will be a nice plus.