If you have not been following the posts by Eric Riha, you really need to do so. They can be found at http://www.wwpd.net/. I strongly encourage folks to read this stuff. Yes, it is math. But if you choose to ignore probabilites in this game, you will never get better. Of course some people play enough that they simply learn the probabilites over time.
Based on Eric's posts and discussion of Expected Value (EV), I created a series of charts which identify the EV for various combinations of Armor Rating, Anti-Armor Rating - all with a Firepower of 3+ (the most common for tanks). Feel free to copy!