In Bourn, you know pretty much what you are going to get. A somewhat above average center fielder (offense and defense combined). In Jackson, you might have a zero, or you might have a center fielder much much better than Bourn (offense and devense combined). But I disagree with BR on his assessment of the odds. I would say that right now, Jackson would be a better than a fringe regular with no improvement with his swing. And I would assess the odds at about one in three that he will be better than Bourn, however you rate Bourne.