Check out this guy's work:
He shoots with the 5D Mark III and Mark II previously. When people say these cameras have poor dynamic range just point them to this guy's work
Nobody is saying 5D Mark II has low dynamic range. Its DR was fine, similar to its competition 4 YEARS AGO!
Now, the new 5D Mark III has much lower DR than its competition. Good photographers can somewhat compensate using HDR techniques, but the facts don't change that 5D Mark III has much lower DR than the competition.
If you are a landscape shooter and are not married to Canon, then you will get much, much more bang for the buck if you use D800/E. OF course, the ultimate for landscape shooters is the MF backs, but that is beyond the scope of the DSLRs.