I've watched Stokes a lot. Sully is a decent comp for him in some ways. Stokes is a tad more athletic, but I think Sully is actually a bit longer. Neither is a major defensive presence, though both put in the effort. I think Stokes is actually a better rebounder (which is saying something), but he hasn't displayed the offensive skillset that Sully has. I think he does have a jumpshot that he isn't allowed to use much (his coach limits him in that respect), but he certainly won't be taking threes anytime soon like Sully does.
Aside from size, Glen Davis and Stokes don't play all that similarly. Stokes knows he's a paint presence, while Davis wants to play like a guard. Stokes is an elite rebounder - arguably the best in college this year.
If you accept my evaluation of Stokes as Sullinger with less (apparent) offensive game, then I think an early-to-mid 2nd-round grade makes sense for him. I think he can be a good bench big, and there's some added upside there depending on whether he has a wider offensive game than he has consistently shown (he flashes certain skills occasionally that make me wonder if this is the case, but that's all they are - flashes).