I've had some superb sessions at Rainbow Beach both north and south of the surf life saving club when I lived in the area 15+ years ago. Conditions can vary greatly depending on what the sand banks are doing. I've never sailed Double Island Point but have kiting friends that reckon the northern side is great on a NE. I don't think you can sail there on a SE as the point is high and throws a big wind shadow, unless you have a kite with 100m lines

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From memory the south side of the point gets very rough in a SE and if you come off, the sweep would probably take you straight into the rocks.
Rainbow Beach is no windier than anywhere else in the area, it is just the position of the wind meter at the light house on top of the cape that leads to the high wind readings.