I agree Alan, when I contemplate a D700 I know I'll miss my 16-85 and 10-24 combination. Yes, I know I can cover those focal lengths, but not with two such small, nicely overlapping, filter capable, lenses. With a 67-77 step up I can even use the same filters. Ratios of 5.3 for the mid-zoom and 2.4 for ultra wide are extremely useful.
There are no comparable FX lenses. Wide zooms are either the 17-35 or 14-24 with ratios of 2.1 and 1.7 and mid is the 24-70 with a ratio of 2.9. Further, the 14-24 takes no filters, the broader mid-zooms are not well rated and 70mm is not long enough, I'd need something into the short tele range. Yes, I can go to my collection of primes, but those two DX lenses have really spoiled me with their excellent optical performance.
Don't forget about the 35-70 2.8!! It has 99% of the optics of the 24-70 and a fraction of the weight. . .
This is one of the primary reasons I haven't jumped ship yet. . .the FX com parables are SO HEAVY and EXPENSIVE! Yes, I'm sure there are IQ advantages, but IMO, probably only for pixel peepers . . .
To that end, my 50 1.4 and 60 2.8 are FX/DX and if I were to switch, I would have to sell the 35 1.8/11-16 2.8/55-200 VR (which are super light and great); comparable purchases would be the 14-24 2.8 ($1799) and 70-300 VR ($550). . .plus a 35-70 2.8 ($500 used). . .so I'd be out $1800, and might be able to get about $850 for all the DX lenses that don't carry over. . .makes me wonder is that extra $1k and extra weight worth it?