I'm not disagreeing with any of that. But like I've said, I don't think the small sample sizes that we have from both pitchers are enough to judge their overall ability. And Chamberlain had a 2.76 ERA last year as a starter. I don't see how that's a downward trend for 2 years unless you thought it was realistic for him to reproduce a sub 0.50 ERA in any kind of extended sample size.
I'm a Red Sox fan, so if anything I'm biased towards them. But I don't believe there's any objective reason to claim that either Buchholz or Chamberlain are significantly more likely to be more reliable than the other next year.
In my opinion, both have great stuff, both have great potential and both have control problems (Buchholz had a 1.38 WHIP last year, a low BABIP and an ugly FIP). I also agree with Spud, that both of them seem to have mental... limitations.