Okafor really had two seasons last year. He started off great as the starting center, among the rookie leaders in points and rebounds.
At some point, the management decided they wanted to see Okafor play alongside Noel. It turned out neither could play the 4. Okafor's numbers, especially rebounds, dropped significantly. Later, he went down with a knee problem, which ended his season.
Okafor's overall numbers last year are probably not representative of what he can do as a starting 5. He was put in a bad situation paired on the floor with Noel. He could not play the 4.
He would probably fare better playing the 5 alongside Amir Johnson, since Amir is more a 4 than a 5 anyways.