I once read years ago and firmly believe it (I paraphrase): "The most important aspect of your photograph is the light, second, your glass and finally your sensor." Orginally the third aspect was film, "sensor" substituted. Personally, I would stay with the D7000 and buy the best glass you can afford. The 24-70 f2.8 would be great and if you can stand prime manual focus lenses, Zeiss FE.2 mount glass (I know, blasphemy!).