@ 105KG what can you control the 6.3m up to in wind strength?
What is the wind strength you are expecting in WA where that sail will be too large?

The guys your size at Sandy Point very rarely use anything smaller than a 5.8m. The only time I have seen them use smaller is if the wind is over 40-45 gusting 50-60Kts and those days are very rare. When Spotty did 50 knots in 2009 he was on a 5m Koncept. I think I have only seen him use a 5m on one other occasion, when it was also gusting 50+ knots.
With the newer sails, I think in the same conditions he might even use a 5.4m, but the best speeds are probably going to be set in less extreme winds where control is better. For comparison, where I was struggling insanely just to survive a run on the course with a 4.4m Koncept down hauled inside out on Spottys 50 knots day, I would probably be a lot more comfortable on the latest 4.6m for sure. On the 35 knots days more recently, I have done almost equal to my PB speeds on the 5.4m Koncept.
In other words, I wouldn't suggest you worry about anything smaller than about 5.8m.

. That should do you well up to 35-40 knots in good really speed conditions. But if you happen to be at Sandy Point on an epic Nuclear day, definitely pack a 5m!

I will watch, cheer you on, and film you from the shelter of the sand dunes!

BTW, AA's sails looked to be all one off customs. I even watched him try them on different masts in 2013. He was looking for something when he played with them on the beach, but it was too subtle for me to see.

That year he only seemed to be using 5.8m when it was windy, but it was not as windy as the record day in 2015.