erm actually no ah im still deliberating over it.. :angel:
I'm one of the D90 + 18-105mm lens kit users who recently made the jump to FF. And I bought the D600 + 24-85mm VR. And to say, it is simply amazing, this FF combo.
Coz the colour reproduction is great, this lens is sharp even at f/5.6-f/8., and the D600 is a real beast in terms of dynamic colour range and autofocusing.
My advice is to go for the D600+24-85mmVR combo. Coz it's really a great combo to have, esp for candid and street photography. And you seldom need the extra 2/3 f-stop; if u need it, just get a prime lens that is f/1.8 or larger. And with the D7100, I wouldn't go for the 17-55mm lens, coz I find it's just not worth it paying over $1500 just for a f/2.8 zoom lens. I would pair the D7100 with the new Sigma 18-35 f/1.8 (when the Nikon mount version becomes available) over this 17-55 f/2.8. Or just wait for the rumoured 18-140mm lens to enter the market before pairing it with the D7100.
At the end of the day, to each his own. Me coming from the DX camera experience with my D90, I treasure the high-ISO capabilities and high dynamic range of the D600. If u r shooting landscapes/cityscapes, streets and candids, then I would recommend getting the FF camera so as to get wide angles without spending too much to buy DX ultra wide-angle lenses. If u r shooting sports/nature/wildlife/birds,, then the D7100 would be the better camera for u, since a 300mm on DX would be an equivalent of 450mm on FX and if the 2x crop is enabled on the D7100, the 300mm would effectively turn into a 600mm FX equivalent, making it ideal for telephoto shooting.