You don't tell us why you feel the need to go to the FX format. That's not uncommon - many folks think it's automatically "better" but in individual cases it may not be the best option.
Given that you want FX, can't run to a D800 (or, presumably, a D4), and you want to stick with CF cards, you don't have much choice - it would have to be the D700.
But... what will a D700 give you? Your lens choices would be very limited. In real terms, a D700 will be about one stop better in noise at high ISO values - and that's pretty much it. I used a D300 and D700 alongside each other for a year or so, and in average-to-good lighting I could see no difference between them.
Have you considered the option of a D300s?
Other than that, you would have to compromise on one or more requirements.
By the way - the DX crop mode of a D600 offers about 10.3MP, not 12.1MP.