D800 & DX-format crop mode

Got my D800 just as I was leaving for NW Ontario where I do a lot of nature photos so I have been taking a lot of my initial D800 shots in the DX-format crop mode. Also to extend reach I have been using the TC 2.0 III paired with the 70-200 VR II lens to give me an effective 600 mm of reach.

It has been qustionned in the forums why anyone would want to use a full fram camera in this way. Well, for this one photographer I am really pleased with results. Any comments or suggestions welcome.

http://jbipix.com/?s=d800+70-200+II+TC+2

Now the question is. Can one camera take the place of two?

. In full frame it excels as did my D700 (sold) and I can crop more for composition.

. In crop DX-format mode, it has faster and more accurate focus. As far as I can test no L/center/ R problems. It handles well and does not really feal that much heavier. In some way I cannot yet define, it yields a more pleasing "look". Soooo, do I keep the D7000 as a low cost backup or do I sell it?

Anyone here done a comparison of the D7000 and D800 in crop mode? Your observations?
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John from Toronto
Best of my D800 - http://jbipix.com/?s=d800
JBIPix Photoblog - http://jbipix.com