Smaller alternatives to the Nikon D600?
For everyday use
You didn't say how small you were prepared to go?
That D600 is a camera with a 35mm sensor.
A Canon 6D would only be about 100g less.
The lightest camera with 35mm Sensor is the Sony RX1 compact; a new version has been announced. No viewfinder though.
If you are prepared to go down to a smaller sensor and still retain good image quality then see the Canon G1-X
http://www.dpreview.com/.../canon_g1x
or even the little Olympus OMD EM5 DSLR.
http://www.dpreview.com/...rs/oly_em5
Then there are the Fuji compacts with fixed prime lenses.
Beyond those you won't get a viewfinder unless you add an EVF to a Sony NEX, and then you're into smaller sensor territory where the Olympus XZ-1 might please you with it's bright f1.8 lens.
Pentax K30 or Pentax K50! Check out weights and dimensions on:
www.pentaximaging.com 1-800-877-0155, or 303-799-8000