Pat,

That is a good point. I'll have to think about how I am going to use the lens afterwards.

I am thinking that I would be stopping either lens, Canon or Sigma, to f/2 or smaller to deliver a certain depth of field which wouldn't be a tremendous gain over the 24-70 f2.8L wide open.

I was leaning towards a Canon EF lens because DPP has lens correction and if I ever go full frame I can keep it.