I was in the same boat a few months ago - had a D90 and jumped on a D700 (used mint). Like you i have zero interest in video, so the D700 was a no brain decision for me. Haven't play with the D600 so far, but, except for the MP, i'm not sure that it's "better" than the D700. You'll be shocked about the low light capabilities of ths machine, if you follow that route.
Nikonians!!! My best investment made after my camera!!!