If Okafor were a legit 7 feet tall without shoes on he'd be going first in the draft and this wouldn't even be up for debate, period.
And I've said many times Okafor is the same size (minus standing reach) as Boogie, where has Boogie gotten the Kings? Best center in the league, yet they're probably going to draft Willie Cauley Stein to protect the paint. It's never been about Okafor's offense, it's about his defense, you're talking like I said he'd be a bust, I said he's Boogie many times over and that also includes needing a big next to him that can defend.
Duncan is 6'10" and change without shoes, and while there's no info on his wingspan or reach he's probably got stretch armstrong arms.