I too am contemplating getting this lens for my D600.
When I was in DX-land, my lens kit was the general 16-85mm, the tele 70-300mm, and a prime 35mm. Jumping to FX, I kept the tele, sold the general zoom and replaced my beloved prime with the equivalent 50mm f1.8G.
And now I have two choices to go about, considering funds are very limited: I could either go the prime way, and get the 28mm f1.8G and the 85mm f1.8G (with the 50 those would make a nice trio), or simply get the 24-85 and sort of repicate what I had with DX.
The reports I'm getting about the 28mm are mixed: not too wide, some field curvature issues (which might make wide aperture use finicky), and it's more expensive than the 24-85. The 85mm gets stellar reviews, but I find it is a very specialized lens, and for portraiture and general tele the 70-300 VR does fine (although I'd love to get a 70-200 f4 VR, too, but it's still a lot of money).
I could also try to get an older general zoom, like the 28-105 AF-D, 24-85 AF-D or 24-120 AF-D, but none of those has VR, and I find that handy. Mixed reviews also don't bring much peace of mind about some of those lenses.
I know the point of going FX is kinda lost here, and this 24-85 might not make the D600 justice, but, as I said, times are tight. My main shooting, without a doubt, is with the nifty fifty, but the tele comes in very handy for portraiture and the eventual daylight kids sports and activities. Likewise, a general zoom may not provide the best IQ or capabilities, but it's priceless for those family times and travelling (I'm a big fan of lightweight lenses for this). Strictly amateur use for me, so heavyweight f2.8 zooms are out of the question due to size, weight and price.
I probably should have gotten the D600 with the kit lens, but money comes slow, and I choose to get the camera first, lens latter.
Having the 50 and the 70-300, what you YOU rather add: the 28mm f1.8G or the 24-85mm VR? Forgot to add, for ultra-wide(ish) I also have a borrowed 20mm f2.8D, so that specialty is covered (although not in spades, I must say).
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