I think the C6916 is a big upgrade from the Z.
I just got mine, rooted it and customized it.
I am running kitkat and the problem I ran into was the sd card thing that everyone ran into. Cant write to SD using apps in kittkat.. BUT If you isntall the sd fix app from google store, it fixes it. I use fx explorer with root..
Works like a charm
To remove all the bloat ware you need root and use a app called System app remover by Jumobile... Best app to remove all apps. But again, you will need to be rooted which is EASY> just look up my tutorial...