handydragonfly said..
Whats the weather like in the bay in Autumn, would a 9m be overpowered, would an 8 be better is the wind range crossover to big?
I'm speaking from limited expeirence (1/2 seasons of winter) but last season, in my opinion, it was actually quite light (12m territory). At least when ever I had a window to get out it was.
Some people live for squall kiting, which is where one waits for a storm to roll in, and kite the front of a rain storm. The wind is extreme, very unpredictable, and best avoided until you have a few years under your belt.
Your current manufacture will publish recommended wind ranges for your current kite. The applicable wind range will differ based on your weight and board, but use it as a guide and calibrate your own experience to the wind range. I.e. if the website says it's good to 22knots, and you went out in 18knots and were over powered, then you know you need to shift the applicable range down.
Then look at the same range for a 9m and an 8m and see what's applicable at the top end. From my perspective, anything over 30knot wind is best avoided, as when it gets to that, it gusts massively. That's just my opinion.