CRC,
I can't speak for everyone who shoots wildlife, of course, but I suspect if funds were unlimited, most of us would own a 1D X along with a few of the super telephoto lenses Canon manufactures.
In the real world, many of us have budgets, sadly, and we have to get by with what we can afford, as my signature demonstrates.
To fordbjr,
When I was selling real estate, the office in which I worked had a very poor camera so I bought my own quality point and shoot. You might be printing much higher quality brochures than we were, but the quality of the original photos really took a hit by the time we printed them or posted them on the MLS site. I was quite proud of the results I got compared to the other agents but the photographs I'm getting from my 70D are a significant better. I'm not sure that improvement would translate well in the real world because of the degradation that happens when printed in brochures or in the MLS, as I posted above.
I said all this to say, unless you are producing very costly brochures, etc., the 70D will be more than adequate and you'll be able to have more fun shooting wildlife for your personal pleasure. This is just one man's opinion, of course. The 6D is a fine camera at an entry level price for FF.
Kim (the male variety) Canon 1DX2 | 1D IV | 16-35 f/4 IS | 24-105 f/4 IS | 100L IS macro | 70-200mm f/2.8L IS II | 100-400Lii | 50 f/1.8 STM | Canon 1.4X III
RRS tripod and monopod | 580EXII | Cinch 1 & Loop 3 Special Edition | Editing Encouraged