The construction of the dedicated slalom iSonic is not designed at all to widthstand all the abuse of high jumps. Better take a Kode which is truly designed for such Bump & Jump use & abuse.
Futura is more user-friendly than iSonic, especially when chop worsens : compare a freeslalom with a pure racing slalom hull. Top end will be higher with iSonic than with Futura in flat to moderate choppy seas provided you have the skills and full camber racing sails, but as soon as chop worsens, a Futura might give you an easier edge in term of top control in difficult conditions.
iSonic 101 is way too big a board for your 54 kg and max sail size of 6.0 m2 IMHO. Better think of an iSonic 76 or 86 slim for your XS light weight with 4.5-6.5m2 sail quiver for example. Make no mistake: iSonic 101 2009 sail range is more like 6.0-8.5 m2 for your XS light weight.