Ok. Fogel is probably an idiot. I wasn't that familiar with his work and was merely trotting it out as an interesting aside. That said, he is not necessarily wrong. Just because one is an idiot and/or an ******* does not make them wrong on every issue.
The south had significantly less to work with than the north did. Thus anything even approaching parity would be a remarkable display of effeciency on their part. The argument (as explained to me by others) was not really that the south was actually an economic powerhouse, but that given what they had, they did remarkably well and probably better than if they had not adopted slavery. That said, I'm way out of my depth here...
Cheers!