Which 24-70?

Personally, I think 70-200 is a little short for wildlife.  The only reason I mentioned the 70-200's is your desire to use a shorter focal length.  For serious wildlife shooting I normally recommend at least 400mm.  More if you can afford it.  The lens I use is the 100-400L, and even on a crop body, I frequently find 400mm too short.  And trust me, I manage to get a lot closer to my wildlife subjects than most folks do.  (You can see some of my wildlife shots in my gallery.)

So, if you're leaning toward a shorter tele zoom, I'd recommend the 70-300L over any of the 70-200L's--simply for the additional 100mm of reach.  Otherwise, go for the 100-400L.  I don't have any experience with the Sigma 150-500, so can't really comment as between it and the 100-400L.  500mm would certainly be nice.  Question is, how sharp is the Sigma at 500mm?