I think Barnes will end up like Luol Deng or Allan Houston.
I think D. Williams will end up like Carmello, only more fierce and with less range. He can overpower some of the SFs and blow by some of the combo forwards. I think SF can be a natural position for him, like it is for Ron Artest. There might be a small, remote chance that he busts and ends up like Al Thornton, but I doubt it given that he's too offensively gifted and efficient. He played under a lot of pressure today.
You know Williams is going for the highest single-season 3-pt shooting percentage in NCAA history, right? He's shooting 60% on a solid number of attempts.