KDevelop and Qt Creator are right now both adding libclang support for autocompletion (and hopefully more of the code model) and both became pretty good in the past. I suggest looking into them, especially as soon as libclang is in.
It's not like KDevelop doesn't have very fully featured auto-completion support right now :).
Its existing C++ smarts are extremely impressive already; the developers are mostly considering libclang to get out of having to maintain their own C++ implementation as time goes on and the language gains more features.
Before anyone feels the need to praise Emacs here: It's been my primary C++ development environment for nearly 15 years. It does it alright, but it's not integrated in the way an IDE is.