I came from the same place as you (D90land) and probably weighed most of the same considerations vis-s-vis D800 vs. D600. As a fellow member of the white-hair brigade, I must admit I did not consider weight even though I usually take two long walks with the camera each day. I'm convinced the D600 is the correct choice for me, at least for now. Among other things going for it, the pixel density is actually slightly less than the D90 which makes the D600 modestly easier to handhold successfully. Also for this reason, it plays nicer with a wider variety of lenses than the D800, which helps ease things on the ancillary expense front. Add "reasonable" file sizes and the D600 approaches "bargain" status. Cheaping out also seemed adaptive behavior at the time since there was always the possibility that, having used the D70 and D90 for about seven years, I might have unwittingly succumbed to the DX "cure", which would have rendered me unfit for FX. Happily, I quickly experienced a return to an older comfort level with FX, a sense of coming home. Suddenly several lenses simply made more sense. And shooting with one of the best DSLR sensors available seems adequate compensation for having saved some money. Long story short - happy camper here - no regrets. I have had multiple successes with the camera and feel I have learned it well enough. Even so, I continually have to remind myself that many of my D90 tricks don't work the same and to shoot accordingly.