let me come to your question from a different direction. i think most of the sailors can be faster with a Futura/Overdrive (personally) well trimmed combo, than with bjorn's iSonic/Reflex set up WITH BJORN'S TRIM, what is the fastest combo and trim on the world right now on the slalom course...
the reason is simply, these top guys whom you check on the pictures make this sport in a different universe.
the point is, im pretty sure for you at age 17 after a serious injury the most important speed factor is the comfort feeling. means if your straps, mastfoot position, sail trimming (as mark mentioned the downhaul above) and harness line position give the lightest feeling for your body when you running down, i think you will be the fastest compare to yourself. for that mission i would put your harness line to the neutral point, where your hands have more or less similar pull of the boom. when your body start to be tiered (as you said to your front arm), you immediately slowing down, even if you cannot recognize.
when you have routine with this "style", you can start to step forward with other trimming details, if you still miss some scary speed experiences