Hey Bigun... I think I replied to you on the Zone???
You gave out more info here... so I'm gonna modify my recommendation. I know you can start smaller than the Avanti.
I didn't realize you were already paddling a 24" wide board.
First of all... to me, you are still a kid

and your confidence leads me to believe that you would be fine on a 9'10 Allwave.
It has a LOT of stability built into the 190 liters... and it will suit you for a while.
Go visit JimK at Extremewindsurfing, in Atlantic City (7079 Black horse Turnpike)
He may be able to set up a demo. He is your size and a good SUP'r... he is a wealth of information and a great guy.
The 9'10 was Jimmy's goto board for a long time... and he is actually bigger than you.
I had a 9'6 Allwave when I weighed 265 lbs.... it was rock solid.