I've owned a pair of 1Dx bodies for over 2 years, and I'm still not convinced I understand the AF system 100%. That said, I picked up a 5DsR last October and feel like the only thing I'm not 100% confident on is how I manage to bump the aperture setting so often. That said, I feel like I've picked up too many lighting modifiers too fast, and I really struggle to look at a potential scene and decide how to light it (or decide what to pack before leaving the house to be ready for said shoot).