RE: Board and Sail
So there's a hire kit operation there in Perth, but they do not have any 120-150 liter boards, is this correct?
If so, are there any other shops that rent gear.
I think if you have those great Perth conditions, you are going to progress very quickly, so a Carve 122/133/144 would seem to give you the stability and volume you need to progress.
Or, pick up a used GO (GO Friendship/Original GO/ newer GO 170) and get yourself up to speed, then spend more for a mid size Carve.
The GO boards are going to need about 0.5 -1.0 m2 larger rigs to really give you top performance, but remember, above 20 knots the GO boards will be getting on the "too large" side of things.
The Go 139 suggested by Crazy Chemical will work, but it's prety wide for > 20 knots sailing, and at your size, the older GO boards may be both faster and more appropriate volume wise.
Hope this helps,