I'll offer my advice since I've sailed Formula for a few seasons, and then decided I didn't want to sail mega rigs and 100cm boards anymore. I swapped to wide slalom. I believe for sailors weighing less than 80kg and sails around 9m, iS122-133 (75-80 wide) is more than enough, no need for 145.
As for the choice between iSonic or Carve/Futura (freeride/"detuned"/"softer"), no one can tell you which is better for you. It's best to try both. Many people find freeride gear easier to sail, therefore earlier planing and faster. Since everyone on this thread is a former Formula sailor, I would guess you'll like "racier" equipment better.