Generally slalom board will get you planning with less wind than freeride board because slalom boards are wider. But on the other side, race sails like Gaastra Vapor are designed for top speed, not for early planning, so with specialized light wind sail you will get planning with less wind. From this you could conclude that best option, for early planning is slalom board with light wind sail, but problem is that slalom boards and light wind sails donít always work very well together.
If you have wind in range from 10 to 15 knots, you can use light wind sail 8.5m≤. But in area where I live wind is gusty, and I believe this is true for most windsurfing spots. This means wind is less than 10 knots for 20 to 30s, and then up to 20 knots for 15 to 20s. Obviously you canít change to smaller gear within 20s, so you must use sail with huge wind range. Specialized light wind sails donít have huge wind range, you get few knots at low end but you lose much more than that at top end.
At the end only really usable option to get planning when wind is less than 10 knot is formula, especially for heavier windsurfers and upwind sailing.