[Edvinas]

If I were to make such a move I'd go for the primes first. Mostly because if I were to switch to FF for the better IQ and AF, I would also want the best IQ from the lenses. Secondly, I'd be holding on to some of my Pentax gear. I'd at least throw in the 50mm f/1.8G with your D800 to start off with so you can have one fast prime to exploit. It's only $215! I guess if you don't use that focal length much though, there wouldn't be much appeal.

Both 70-200mm and 24-70mm are excellent lenses. I have no experience with 70-200mm, however I have 24-70mm and it definitely exceeded my expectations. I was expecting quality something like 16-50mm on Pentax APS-C and I was completely wrong. Nikon FF + 24-70 Nikkor is so good that I've cancelled my plans to buy primes in that range.