Just how good is Justin Upton?

Buster Olney writes about possible trade partnersInsider for the Arizona Diamondbacks if they decide to deal Justin Upton. Jim Bowden lists five potential trades for UptonInsider. (Both are ESPN Insider pieces.)

Here's my question: Who, exactly, is Justin Upton?

1. Is he a 24-year-old superstar-in-waiting?

2. Or has he already maxed out and reached his peak?

His trade value hinges on how a potential suitor views Upton's future. He turns 25 in August; in general, young players get better, peaking at 26 to 28 years of age. But that doesn’t mean Upton is guaranteed to improve moving forward. When Upton hit .300/.366/.532 as a 21-year-old in 2009, expectations flew off the charts. While he finished fourth in the MVP voting in 2011, his batting line was essentially a replica of 2009: .289/.369/.529. A thumb injury hampered Upton at the start of 2012, and his numbers are down so far.

So ... who will Justin Upton grow up to be?

I wanted to find a list of similar hitters. In 2011 and 2012 (his age 23 and 24 seasons), Upton has walked in 9.2 percent of his plate appearances and struck out in 19.9 percent. I began by searching for all hitters since 1990 in their 23-25 seasons who walked in 8-10 percent of their PAs and struck out in 18-22 percent of their PAs. I culled out the guys who weren't power hitters. Here's the list (plus a few others who just missed one or two of the cutoff percentages):

That seems like a pretty solid list of comparables. Upton's wRC+ actually ranks fourth on the list. What we generally have, however, is a list of very good hitters opposed to the game's elite hitters. Yes, Larry Walker had an MVP season in Colorado. Derrek Lee had that MVP-caliber season with the Cubs in 2005. Adrian Gonzalez has certainly been one of the game's best hitters in recent seasons.

However, of the best 30 hitters since 1990 during their 25-27 seasons (the years, after 2012, that a team acquiring Upton would be getting under his current contract), only one of the guys on the above list made it: Matt Kemp, and he ranks 28th. (List sorted by FanGraphs' wRC+.) We're talking guys like Frank Thomas, pre-PEDs Barry Bonds, Albert Pujols, Joey Votto, Alex Rodriguez, Ryan Braun, Lance Berkman, Ken Griffey Jr., Chipper Jones and Miguel Cabrera.

I don't see Upton being in that class. He's yet to post an on-base percentage over .370. He's played in a hitter-friendly park -- his career OPS at home is .924 and .744 on the road. Yes, you have to factor that a large percentage of his road games are played at Petco, AT&T Park and Dodger Stadium, tough places to hit (although he's hit well in Petco, with an OPS over .900).

Another consideration: While Upton played 159 games last season, he missed 24 in 2009 and 29 in 2010, and while he's missed just six games this year, he's battled injuries. A young player with durability issues doesn't usually turn into a more durable player as he ages.

Look, there will be a team out there that believes Upton will turn the corner like Kemp did a year ago. Or blossom into a right-field version of Jim Edmonds (who suddenly started walking a lot more after he turned 30). My take is that Upton is a very good hitter as opposed to a superstar hitter, although a guy certainly capable of that one monster, MVP season. That's still something every team would want, and Upton's salary isn't prohibitive. He's a good defensive right fielder. It's going to take at least two top prospects or young players to get him, maybe more. Are you willing to do that?