Hi Mate. I'm a 70kg sailor, so I can't give you any advice about equipment. I recommend you re-ask this question in the General forum as there will be freeride/slalom sailors on there that will be your weight and can supply good advice.
However, Black Point is pretty flat, and places like Port Vincent and Stansbury even flatter. There is a crew at Stansbury if you want somebody to sail with. Between 2-10 sailors sail there on any given session in summer. Infact, the whole west coast of the Gulf is pretty flat relative to other places (ie: Metro, Boggy etc), so any board that is wider than normal (which the Magics are) is going to sail better on the west coast of the Gulf (you don't want a wide board in chop).
Good luck. We'll no doubt meet

J