I think you guys are aiming a bit high on RBI's. As far as I remember, my Cubbies still don't have a real leadoff hitter. They may have Grudz hitting leadoff, and he did a good job last year, but I just don't know. Patterson will be hitting second behind Grudz, or else he may be forced to bat leadoff (and I have to assume he'll bat leadoff whenever Grudz isn't starting, unless maybe they start Goodwin in LF instead of rickety Moises Alou).
All-in-all, even with his power, I can't imagine him getting 100RBI's.
I'd say .275, 25 HR, 75 RBI, 100 R, 20 SB.
He shows flashes of being a .300 hitter, and then he goes on slumps where he seems to strikeout 3 times a game. Once he gets some consistency, and a little bit more plate discipline, he could easily be better than Beltran.