Ok, I just found the study and I was slightly wrong. The worst batting order (order of ascending on-base) finished 6 games behind a "standard" order. The best batting order (descending on-base), though, was less than one game different than the "standard" order. Here's the study:
<a href="http://www.alumni.caltech.edu/~raj/writing/BattingOrder.html" target="_blank">http://www.alumni.caltech.edu/~raj/writing/BattingOrder.html</a>