I have both the D700 & D800 and think they are both excellent cameras. I would say the dynamic range on the D800 is better and I like the lower base ISO on the D800 for the type of landscape shots I take, mainly long exposures.
The 14-24 lens is excellent and I use the Lee SW150 filter kit with mine which is also excellent. I would see what focal length lens you use the most currently and replicate that on an FX camera. For me I use my 24-70 the most probably at 24mm. I would also check out the 16-35 f4 VR as an option as it takes filters and ive seen some excellent examples from it checkout here. Ian used it on his D700 and now on his D800 and would give you some great examples IMHO.
I think the D800 will give the ability to use the different crop modes and this also worth considering.
Sounds like a fantastic trip.
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