Here, two parameters have changed that lead me to conclude that Zito's performance will not hold up in Texas.  First, his numbers at Texas have been far worse the last few years (5.28 E.R.A. in 2004-2006, although he was at 3.74 this year).  If I were Zito, I would be concerned by the fact that my stuff and control has declined in the past few years which makes me increasingly susceptible to Ameriquest's potential terrors for pitchers.  

Second, and most importantly, it is hard to get an accurate picture of how Zito will fare pitching half his games in Ameriquest by his pitching in a very few games there (7 games in the last 3 years for example.)  Pitchers who have pitched in Coors Field and Ameriquest have complained about the cumulative effect of pitching so many games there.  I think this cumulative effect will be worse for Zito based on two factors: he consistently throws among the most pitches of any pitcher in baseball and he is a person who appears to be oversensitive when fialure comes along.  I think Zito will suffer greatly from both mental and physical fatigue in Ameriquest.  

Of course, I am making subjective judgments when the raw data does not support my theory, something my empirical self is uncomfortable with.  I may end up being completely wrong, but I predict that Zito will be a disaster for Texas if they sign him.  It just seems too much like the Eric Milton in Cincinnati or Darryl Kile in Colarado signings to me, made worse by the fact that Zito will be getting twice the number of years and quadruple the amount of money.

Any significant look at Ameriquest will tell you that it's a hitter's paradise.  Any significant look at the Coliseum will tell you that it's a pitcher's park (or, recently, relatively run-neutral).  Barry Zito is a flyball pitcher.  Flyball pitchers, as a population, do not do well in Ameriquest.  Taking one pitcher's performance there in an isolated sample size doesn't give you much to base predictions of future performance on, even for that one particular pitcher.  

However, looking at larger issues that do have a stronger statistical foundation will give you a better prediction than just looking at Zito's individual situation.  It sounds backwards, but it's true.  Until we have reason to believe that for some reason, Barry Zito will always pitch well in Ameriquest (which would basically take a sample size of several years of pitching at home there), you can't point at this one particular case and say, "Well he's gonna pitch well there because he did it before".