1) 1.3 crop I want this for using my 16-35 f2.8 as a walkaround effectively 20-48mm and for getting the extra reach on using long lenses. but has better IQ than the 1.6 crops
2) AF at f8 long lenses and teleconverters coupled with item 1 it stomps the 1Dx on the long end.
Ok gotcha on the (1) though I just read surprisingly on the-digital-picture.com that the current 7D has better resolution than the 1D IV (however) it is not as sharp with the settings on 1 but you sure get the tradeoff with that 1.6 extra reach so know what you mean on item (2). Used a 400mm today on the 7D bringing it to a 640 - that was a treat with wildlife photos. Also used the 16-35 mkii like you with the 7D - most pleased. If you are concerned with IQ, check out the DLA's on your camera choices as well (1DIII, 1D IV, 7D, etc). Though diffraction doesn't have a huge impact it can affect IQ as well. it's just one more thing compounded to reduce the IQ of your overall picture