I moved up from D70 to D300 several years ago then moved laterally to D90 and stayed there until gearenvysyndrome (popularly known in these here parts as NAS - Nikon Acquisition Syndrome) got the better of me and I plumped for a D600. My shooting profile probably matches yours. Where I am slightly more 'advanced' (perhaps the better term would be lost to the disease) is in having acquired lenses over the years in a manner that made going FX inevitable and seamless. You may find with your two primes that you are suddenly in need of a longer lens to get you to the same place as the 85 could get you mounted on the D70s. Even though I had the lenses I did dither over the reach/resolution question. Cutting to the chase, I think the D600 holds my personal record for the most immediate, sharpest end of buyer's remorse. I think it was around frame 50 (the first two days were heavily overcast and useful mainly for playing around with iso 3200 and determining that it is indeed a viable option) finally in good light. I went out to shoot the D600 24-85 against the D90 18/70. The colors of the D600 were far more natural. Also, I had inadvertently shot a few frames underexposed at base iso and found that I could bring up the shadows up in PP nearly three stops without any visible noise penalty. Deal done. The next to last shoot I did was in a relatively dark room and I was forced to shoot iso 6400, f3.5, 1/80. Simply unimaginable on a D70 or D70s. Horizons widen in more ways than one with this camera. That said, this is a more exacting camera to shoot well than its 6mp antecedents. Optimizing detail sharpness demands it to be held as stably as you can manage. If you already have developed a tripod or monopod habit, you'll be fine.