He isn't as quick as say Bailly but he isn't a slouch either. I think his towering presence gives off the impression he is slow, and that is not the case. The only weakness he has is that passing is basic, in that he will go for the easy option rather than trying anything silly. Which considering how many of our CB's just hoof it upfront, it would be a welcome change.
Here for example was his Barcelona debut (I think) against Getafe (where he was voted MOM). You can see his aerial presence and the fact he isn't afraid to play high up the pitch when needed:
Below is against Valencia, where he was good but you see his passing is very basic and needs work. So I think this is a fair showing of both his good and bad attributes: