2) determine the difference in miles that you would get w/ AA vs. AM. In terms of spending the miles, generally speaking, these days AA and AM require somewhat similar miles (unless you have specific redemption in mind in which case you should include that in your calculation).
One thing to consider here is that AA has recently devalued their chart. CXs redemption chart hasn't changed for....2 decades maybe?
I have no inside knowledge but don't bank on that CX redemption chart staying the same for much longer.