So if I use my 70-200 2.8 but it's a little far so I crop it how does that compare to a natural 400 2.8 or for that matter the 200 end of the 70-200 with the 2x teleconverter? Iq? The 400 2.8 is massively expensive so to spend 11,000 vs a crop or a 2x is a tough decision. Thoughts?