Looking to sell my D7000 & go with the D600 but I am quite concerned re. losing the 1.5 DX factor. I do a lot of bird & BIF photography & am happy to turn my 500mm into a 750mm BEFORE even adding the 1.4X or 1.7X. So reach is very important to me. Even with this I often still need to do some serious cropping in PS to get the subject sized right. Here's the question: with the additional MPs of the D600 will I be able to get close to the same final cropped image with excellent IQ? Yes, I know the D800 would be better but I need the higher FPS of the D600 & don't want to deal with the huge 36MP files etc.