A lot of light wind riding has to do with proper body position, board and kite technique. Keeping the board flat and not trying to go upwind too much really helps. I can ride the 13.5 Cult or 14 Park in 8.5 knots with a 134 Axon board and stay upwind no problem. (Comments that the Park has no bottom-end are total BS) But this took a lot of days of teaching and riding in uber-light winds to get the technique. A big board definitely helps (love the LF 145 WLF) and a race board would be money.

A big part of riding the Park, Cult, Helix etc is that you should always have at least 1 to 2 inches of the de-power strap pulled and make sure to sheet out on the upstroke. Otherwise, the Cult especially will tend to backstall. Also when sining bridle kites, the technique for generating apparent wind is much different than for C-kites. With C-kites you can use a standard up/down sining motion. For bridled kites it is important to make an aggressive downstroke and sheeting in hard when the kite is at it's fastest, then let up on the sheeting and allow the kite to fly at a 30 to 40 degree angle back to the top of the window. This by reducing the climb rate and angle of attack this enables the kite to generate more apparent wind. Also at JI and other spots where the wind tends to be stronger higher up using the top 1/3 of the wind window to generate power really helps.

I made a 12m Helix on long lines work for a long time, so I wouldn't suggest getting a bigger kite unless you get a kite like the 18m North Dyno or 17m Ozone. A big board and good technique will be a lot cheaper though.

(Thanks Zach!)