If you guys are still curious about the difference between the Bill and William I can give you my feedback/knowledge about them.
To start out, both boards are the same exact shape, but what is on the inside of the boards is extremely different.
The bill is just a normal foam core board, while the WIlliam has the new Ronix Intelligent core.
The bill is more flexible, while the William is super stiff and responsive. The Intelligent core uses a mix of wood, foam, and carbon fiber to increase speed, durability, and overall response of the board.
I have ridden both, and they are both great! The bill is a blast at the cable- flex, soft landings, the whole nine yards- and still a great board for the boat. Very consistent and overall good at everything.
The William is MUCH faster, more explosive due to the new core. I was blown away by it when I first rode one. I let my line out 5 more feet and still was cruising right across the wake.
Overall the William is just a supercharged Bill board. Both awesome new boards to the line this year!