Hi pratajp,
The Instincts easily make a 2 kite quiver, especially the Edge II's. It more depends on the wind ranges at your local beach. If you live in a lighter wind location, then the 13 and 9 would be perfect. if you lived somewhere where the wind is strong like WA, then perhaps an 11 and 7 would be ideal.
I have ridden all sizes and cannot tell you the top end wind range of any of the kites. I have ridden the 13m Edge II in 25 knots without the use of the trim for depower and have been quite comfortable.
I have flown the 11m in 30 knots and a friend of mine (same weight) in 30-35 knots, in 30 knots the kite needs no depower adjustments but at 35 knots you need about 4 inches of depower. (It is quite comfortable to ride in 30 knots, not in damage control mode like on other kites), The stronger the wind, the scarier the jumps get.
The most amazing thing about the Instincts Edge's is that the performance and stability of the canopy does not change in stronger winds, they just keep performing reliably regardless of wind speed. Only thing that changes is the size of the jumps, you just never get out of control on them!
I have flown the 9m in 30 knots and it was so easy it was ridiculous. I will hazard a guess that it would be comfortable into the high 30's. Again, the stronger the wind, the more massive the jumps, especially on this kite!
The 7m is the sweetest of them all and not in the least bit squirrelly. Super stable and the easiest 7m I have flown when you consider it's awesome potential for stratospheric jumps. I got going in around 22 knots but was working it. It starts to become playful in around 30 knots and I would think it would start to get nicely powered in around 35-40. By the feel of the kite, I think low to mid 40 knots may be possible but I am only hypothesizing as we just dont get wind that strong here to test it. (I wish

)
I weigh 87 kilos and consider my self to be a very proficient rider especially in stronger winds so subtract a few knots for your weight and skill level if required.
All of the Edge's are phenomenal kites with unprecedented wind ranges. I would go as far as to say with two boards and an 11m Edge II, I would be right from 13knots until 35knots quite comfortably, but why do that to yourself and deny yourself the experience of flying the 9 or the 7.
We have a full range of all sizes to demo including the edge II, 7m for the winter storms here in Perth.
Good winds,