I think that lowering the boom, putting in a smaller fin and making your harness lines a bit longer will improve your control a lot in strong winds. Also, when you are sailing, and you see a chopp coming, antecipate your move and sort of twist your body forward, this way you will keep the nose of the board down and maintain speed. Also, there are a lot of people that think that when the wind is stronger you should downhall your sail a lot more, that is not always true, and sometimes when you do that, the nose of your board will rise more. So never overdownhall your sail.
Valeu e abracos,