A couple of key differences. Howard struck out a ton but was still a couple of % points lower than Jackson. He also walked a decent amount more and of course already had killer power.
Still, Howard is one of the exceptions of huge strikeout guys and I don't think we should be predicting Howard type power from Jackson.
Well, he specifically asked for any exceptions. And Howard struck out at 26% as a 22-year-old. Jackson struck out 27% as a 20-year-old. I'd actually take Jackson's over Howard's.