5 ounces is not so insignificant.
Of course it is, outside of very specific circumstances and requirements.
For serious backpackers and trekkers who shave off excess weight from their gear by shortening shoelaces and removing labels from their clothing , this could be a lifesaver.
I really don't see the relevance of that situation to pottering around taking pictures. Astronauts aren't allowed to take much weight up to the ISS either, but that's hardly significant to the discussion.
By switching from D800 to D600, one can do also away with those bulky CF cards and achieve even greater weight savings.
"Bulky CF cards"?
Seriously? If the heft of a CF card is a problem, I think knitting might be a better distraction - you can get
carbon fibre knitting needles if the old-fashioned ones are just
too much...
Just for a sense of perspective, I've just weighed my (empty of cash)
wallet and it came in at just under 5 ounces - can't recall the last time I felt that the weight of my wallet was an unacceptable burden.
I'm a fifty two year old man, healthy but not remotely obsessive about keeping fit, and I have no problem with spending hours (and I mean
hours) in the field with a gripped 7D, Siggy 120-300mm f/2.8 OS and (usually) 2x TC plus everything else I might need for the day (I don't spend my time within a few minutes of the car, I walk for miles - double figures are not unusual): the Siggy replaced a
much (pounds) lighter 100-400mm at the beginning of the year, and I simply don't notice the extra weight. Using (as I do) a
neoprene sling-type camera strap will easily and completely neutralise a 5 ounce weight difference between a D600 and a D800.
Sorry, but to suggest that such a difference will be a deal-breaker except in extremely specific circumstances (none of which we know to apply to the OP's situation), is just daft.
To use an apposite Americanism here, some of you need to
man up!