I'm currently using a 70-200MII + 2xIII for birding and I'm wondering how bad will I miss my 7D by upgrading to 5DMIII?
A super-tele is definitely a big NO for me.
I know that by going from crop to FF, I'll lose the extra reach. The subject will be smaller in the viewfinder and the extra 4mp of the 5DMIII will not be much of a help.
However, I've seen in another thread here in CR discussing the comparison in DPReview between 5DMIII and D800 by enlarging the 5DMIII image with a slight quality loss on the Canon side.
So, back to my question, how much can we enlarge 5DMIII images until the quality degrades to a level comparable to a 7D image?