Don't be fooled by the width of a board to say it's closer to a slalom or to a Formula. Rails shape and thickness, scoop-rocker line, outline, etc... are all key features as well.
2007 iSonic 145 : (free)Formula >>> slalom
2008 iSonic 144 : slalom >>> (free)Formula
For a heavy weight >90 kg, iSonic 144 is spot on WRT iSonic 133 IMHO as a large slalom board.