Nate Silver compares the merits of a Fukudome/Murton center/right combination against lefties, versus a Johnson/Murton combo:

However, there is another option in the form of Matt Murton, who is around .12 runs per game better than Johnson against left-handed pitching — the equivalent of about 20 runs per 162 games — and fully .20 runs better than Pie. Can Murton play center? Probably not in a way that most teams are willing to tolerate. But Murton could play right field — and Kosuke Fukudome could play center, which by most accounts he was able to handle competently in Japan. It’s hard to imagine that a Johnson/Fukudome outfield is fully 20 runs per season better with the glove than Fukudome/Murton; it’s not like Reed Johnson is Gary Maddox out thee. And here, the clubhouse externalities work in the opposite direction, because by acquiring Johnson, you’ve made clear to Murton just how unimportant a part of the club’s future he is.

It’s not a bad acquisition in the abstract so much as an uncreative use of resources, which has become something of a hallmark for the Cubs.

The last line really rings true, doesn't it?

Between all four of the players in question - Pie, Fukudome, Johnson, and Murton - Murton has the superior bat against lefties, and there's no reason to think he won't continue to do so.  Working him into the lineup against southpaws would be a benefit to the Cubs in those games.  Unfortunately, Murton is a defensive liability.

Baseball Prospectus has Murton and Johnson as about average fielders at left field (based on FRAA), although baseball wisdom holds that Johnson is, while not a terribly good CF, at least capable of credibly playing the position.  Murton is not.

The question is, how good of a center fielder is Fukudome?  A center/right field of Fukudome/Murton would be worse than Johnson/Fukudome, but by how much?  I'm tempted to say that it would not be enough to offset the real gains that Murton's projected .310/.380/.488 line against lefties would bring, over Johnson's .278/.346/.416 projection.

Worth pointing out: Johnson's projection doesn't match his career performance against southpaws, who he's hit .308/.371/.462 against in his career.  Murton's career split against lefties is just a touch better than his PECOTA projection.

Either way, Johnson definitely has value as a backup for the Cubs, as he's the only bench OF who can credibly play all three slots, though I guess Cedeno's supposed to be able to play center.

So what do you all think?  Murton or Johnson?