i fly my 6.6 with very strong brake lines(and in light wind, 4-11kn, +11kn i extend the brake lines without loosing depower) if they're to long, the kite will slow down and won't create the lift that the blade must give for doing high jumps! It gives also a quicker turning speed and easier to take off!
many people think that long brake lines gives a better result but i'm not agree with this!