Since the field of view will be wider on the Fx camera, some of your choices might be different than what you preferred on your D300. If you really need 35mm, Sigma's 35mm 1.4 is the top rated 35 mm lens now, plus a relative bargain. A comment above about the D600 having the same AF system, might have confused things. It has the same base AF system as the D7000, not the top of the line system of the D4/D800.
Regarding Rockwell, he is an entertainer and his income is based on getting traffic for his site so expresses factually questionable comments intended to generate controversy. That causes people to post links back to his comments on other forums. That is a common technique of building site visits, and very manipulative. For advice, you will not find a forum or community with more Nikon knowledge, and helpful balanced attitude than right here on Nikonians. His site might look crude and unsophisticated but it generates a great deal of money from commissions on sales through the many links he provides to dealers he has contracts with. The stock and availability on the those sales sites greatly influence his recommendations. For example,he gave a rave review initially for the D800 before ever seeing one but soon discovered that demand was far greater than supply meaning he would not get commissions for cameras that were not in stock, he suddenly tried every way to claim the D800 was the worst camera available and the new Canon 5DIII which were sitting on shelves unsold, became his strong recommendation. That sort of behavior has been seen throughout his career as web blogger. He has been honest enough to admit, however, that his blog is not to be taken as factual.
I prefer the D800 and love mine but both the D600 and D800 are capable of world class images with stunning dynamic range and low noise unmatched in DSLRs, beautiful color and vastly superior image quality compared to the D300m or any other current or past camera. What subjects were you intending the 400mm to be use for? Which 400? Stan St Petersburg Russia