I am no pro in this arena, but... I have been riding strapless boards for about a year and try every board that my friends will allow me to (that makes maybe 25 boards).
I can say that I was able to try the 6.0 NSP fish (slightly smaller than the one you mention) and that I really enjoyed the ride for small/medium waves. The board carved really nicely and felt very nice. I can't see you being overpowered in it in 20 knots, not with the right size kite.
In terms of light wind, my buddy that let me demo it (thanks Chase) weighs about 190.
He uses the board as a light wind board with no problems.
I know that's pretty limited info, but it is better than nothing, (right?).
The NSP also seemed pretty tough. I am somewhat surprised more people haven't mentioned that board. Anyway, definitely not a pimp post, just the truth. I am considering buying the 6" NSP right now and trading in my 5"11 Jimmy Lewis Fish for it. I enjoyed the NSP much more. It felt like a more natural and loose carver, compared to the JL Fish. Also, the NSP "stays stuck" to the water much better (when heading out over the waves). My Jimmy is so fast and has so much volume/surface area in the tail it wants to get airborn.
Anyway, hope that helps, even if only a little.
I don't think the NSP will prove to be a total dog or waste of money, is what I am saying.
Is it the best board in the world?, doubtful, but you were asking if it would work for kiting... hell yeah.