To my mind the 1 line infantry vs. 1 line infantry tests are conclusive. They're too one-sided not to involve stat bonuses, there's no "AI" involved really, except perhaps in timing the polish-the-human-off charge, by which point a clear victory is already guaranteed.

The problem is if the AI and the stat bonuses are tied to one another. A lot of us are going to want a stat-neutral, maximum AI intelligence option. Is that medium? Because it isn't likely to be stat neutral on Hard/VH. Hopefully they haven't been tied together inextricably in an attempt to disguise the stat-neutral performance of the best AI.