I have also tried many board combination for light winds and i'll have to admit that the monster door is the earliest planing tool for the job, however, it does feel like riding an aircraft carrier and it turns like one too, absolutely no fun at all.
I almost given up on light wind riding. But, in the last few months i've been useing a 2009 Naish 5.7 global fish and i feel i'm in love again. In combination with my 13.5 Kahoona it makes the 10-13 knots days really fun to ride. For even lighter winds i just remove the two rear fins and i can ride it from almost 8 knots. I use it both strapped and unstrapped and in betwin (i really like to ride it with the front footstrap only).
Now i don't even bother useing my twin tip in anything lower than 17knots.
Yesterday i also did a comparison back to back betwin my 13.5 Kahoona and my friends 17 Zephyr in 9-12 knots of wind. Well all i can say is that after that i have a smile permenatly marked in my face from ear to ear. I lost in the really lower puffs (8-9knots) BUT when the wind hit the 10knots mark my Kahoona over took the Zephyr in speed of sailing, turning, upwind and fun factor. I'm 90kg and the board i used was the 5.7 fish in quad fin configuration with only the front foot strap installed.