I guess I'm so used to FF after all the years I'm reluctant to change back. Used to the focal lengths in particular, especially since I tend to shoot wide. I might look into Nikon primes as an alternative with the d600. Weight is my biggest factor that makes me want to switch to Sony's offering, but perhaps a d600 with a couple primes will be alright.

Having not kept up to date with bodies, is there a small APSC body that has equal or better IQ to the d600 and also equal or better ISO handling? (I shoot a lot of low light too)