Commom conception is that footstraps placed further back are best for speed. I have mine both all forward just as a starting point on my iS105.
I suppose you played with them could you share your findings?
What kind of wind speed are you refering to to consider a 8.3 sail too big?
On your favourite stance I fully agree, hard to keep the board that way, very demanding indeed.
I'll take your word as I have no gps