My BB is a threaded 68 mm English with a Megaexo FSA crank. I want to change it to a Dura ace and have a couple questions:

1. I'll probably go with a DA 9000, but will past models (7800, 7900) also work?
2. Is it necessary to change the BB bearing cup since I assume both are 24 mm spindles? If so, stick with DA cup or upgrade to a fancier ceramic type?