Zoom lens for Nikon D600
Not a direct answer to your question, but…
I was in the same boat, looking to upgrade from D80 to D600. After walking around the store with the D600+24-120 for about 15 minutes I decided the combo was just too bulky and heavy. I travel light = one zoom, one prime, max. Plus, for me, 120mm is a bit limiting. The 28-300 is about the same size, but of course more of a compromise optically.
So… I ended up buying a D7000 for less than half the cost at current prices.
I know the D7k is about to be replaced, but it’s such a jump up from the D80 in every respect. I love it so far, though the AF is a challenge, as many have noted.