Freeride sails will work fine on an iSonic in moderate winds. However, when at the upper limits (wind, speed, chop), a cambered sail will be more stable, more forgiving and easier to handle than a comparable sized freeride sail, and FASTER.
In light winds, the cambered sail should have a deeper and more stable foil, which should provide more power and earlier planing.
Others that are fans of non-cambered sails may have a different opinion, but the vast majority (98%) of slalom and formula racers use cambered sails. The % is a wild guess.
I don't know much about weed fins. The few that I have had, had large foils for increased power since the depth of the fin was limited. This would add more drag and would probably be slower. Someone else with more experience with weed fins can add to this.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.