BTW, as to the socially conservative category, just look at Newt's marital history to see where he really stands on that issue.
I don't think you can judge someone's views based on their personal weaknesses. And, remember, "Jon Carry" (Kerry) very nearly was elected despite his numerous personal issues.
I think Romney is a possibility, but he is kind of an unknown quantity. He will need to start doing a lot of national media exposure, and soon, if he wants to have a shot.
And, given Clinton's rapid rise in 1990-91, I think you also have to give some consideration to Sonny Perdue. He seems to have the important ability to bring in the blue dog Democrats.