In our experience, C&P is much easier than the other classes listed. DS found algebra I difficult as it was his first AoPS course and hard to adjust. Algebra II was much easier than algebra I but still harder and more time consuming that C&P. Richard Rucszyk (sp?) says geometry is the hardest of the intro courses. DS agrees with that and spent many hours a week on geometry.
I think it's a good idea to substitute school math with AoPS since it provides better instruction and deeper math for kids who love math. If your DS loves doing C&P, then the workload might be manageable during the year. Depends on the kid.
