We carry slingshot and ronix in our store and am required to demo each board so we can get to know our products. Like said above the Response is a relatively close board to the William.
With the William as you know you have the aggressive continuous rocker. The Response is gonna have that same aggressive rocker if not more than the William. The response you'll find to be a medium to stiffer flex board, William itself is relatively stiff with the intelligent core. So if your looking for the board like the William but with flex the response would be a great choice.
http://lhmwakeshop.com/2015-slingsho...onse-wakeboard
If your looking for the closest thing to the William but flexier, take a look at the Bill board from ronix as well.
http://lhmwakeshop.com/2015-ronix-bill-atr-s-wakeboard
Let us know if you have any questions!
Will