The CA are pretty much unstoppable once you upgrade their armour. In my current Armenian campaign I am using them even against heavy Roman cavalry. I just leave them on skirmish for while and then when they get cornered at the edge of the map I just turn the skirmish mode off and charge the romans. I suffer some casualties but victory is certain.

My army is made almost entirely of CA and I control all of asia minor, the middle east and North Africa up till carthage.