This is a bit of a cross platform discussion, so please bear with me.
I have been looking at a longer zoom, to either compliment or replace my Sigma 70-200 F2.8. I have looked at the 150-500 Sigma and the Sony 70-400G F4-5.6 lens (FYI, the Sony 70-400 would be equivalent (in market position and intended usage) to the Canon 100-400 and I am assuming the 80-400 Nikon lens, but is slightly faster wide open (F4 V F4.5)).
The big issue for me is that the Sony lens is approximately $1000 more then the Sigma 150-500. If I went for it I may have to sell some other equipment.
For those of you who own the OEM Canon or Nikon lenses, do you still own a 70-200 F2.8? Do you find that you really do not use (or you have no use for) a 70-200 F2.8?
Any advice or comments welcome (please do not let this become a gear fan boi thread, please keep it general)