If it blew 10-15 all day, you'd never beat the ARC boats. The year that Tina and I did so well, we went down the river on the Cap with the kite up, up-wind in light air, for 90% of the race. We pulled that off with the small set of sails and a super loose rig - the big spin wouldn't have sailed that high. We passed the last monohull and led the race for over an hour, nobody in sight behind us... alone... until I did something stupid that resulted in a broken tiller extension just before the breeze filled in. We could only single-trap; the 30 passed us with two miles to go, the 27 was next, and we fought an A-cat all the way to the finish. If the breeze had been on for the whole trip (i.e., for the ARCs), we'd have been much farther back, I expect.

Like Ding says; you never know what you're going to get, and sometimes fortune favors odd combinations.