I've been really enjoying using my D60 with a sigma 105mm 2.8 macro lens and Nikon 55-200mm and I've been very happy with the results. It's wildlife photography; mostly plants, fungi and birds. I am pleased with the D60 photos but was considering an upgrade for these reasons: higher resolution for cropping, ability to shoot video, live view perhaps with an articulated screen, higher iso which is less grainy and means I don't have to rely on flash, and for increased sharpness and overall image quality-though I am not sure whether this would greatly increase from what I've read.
I am looking at either the D7100 or the D5500 (also considered an old full frame like a D600?). All advice much appreciated on whether an upgrade would be worth it in terms of image quality and which model would be best, or alternatively whether I should invest in a longer telephoto for birds instead.
Thanks for any help