Pot,
All I can say is that in my many CD-ROM games mostly with a wide variety of catchers arms Hal (or the computer manager) seems much too conservative for me on the base paths. My current league is a draft league with the Hall of Fame cards and the Heroes set (basically similar to ATG, but with a lot less players, which is part of the reason why I like playing here at TSN. The sheer number of players that is...) and when the computer manager is set to "Conservative" for base running and stealing it is much too conservative for my liking. I have seen the computer manager not steal when there is an 80% chance of success, and I don't mean with the team's best power hitter up and two outs either. I can not say setting your base running to "Aggressive" means you will win more games every time because I have never conducted a study. But I have seen the computer manager (Hal) manage much too conservatively on the base paths.
I do remember seeing a study of outfielders' arms that concluded that they are way overrated. And this study was conducted with thousands (if not tens of thousands) of games. I think it was posted at the Strat-O-Matic Fan Forum.