Definitely. Much more so than in the video, where you are limited by the 8-bit file format.
I think this one is good: http://www.fredmiranda.com/5DIII-D800/index_controlled-tests.html
See how much cleaner and more usable the shadows are on the D800? It makes a huge difference for what I shoot.
I've done some dynamic range comparisons for myself (but only compared to the older 5D2, not the new 5D3) but haven't put them up yet.