I don't think Delmon will put up the #s that you might expect. He'll have solid speed stats, but I don't believe he will show much power. I see him with about 15 hr's and 20-30 sbs, if he finds a place to get him 500+ abs.
As far as 2 prospects with highest impact, I'm going with BJ Upton and the other kid from Arizona Quentin. I think Young will struggle with avg, which will keep him in the bottom of the order. Quentin, however, will provide both power and avg, which makes him the better prospect IMO.
Also, don't forget about Kendrick, who could flirt with a batting title this year.