Is Nikon D3 still a good buy?

Yes an excellent camera.  Do not listen to all the horse-scheisse that is spilled on sites like this regarding the dire need for huge sensors.  Chasing the latest, greatest and largest high def beasts can make you crazy (and broke), ha ha.

Maybe in some cases for some people they may need 24-36 mp, but for the majority of us 12K is perfect.   For the size of the prints I sell and the type of photography I pursue, 12K in right on the mark.  Check out Carl Groble's blog, http://karlgrobl.com/blog/ He travels the world running highly paid tours and also shoots professionally for NGO's.  He is on the road 8 months of the year and makes his living with his cameras.  He ONLY ever shoots JPEGS and uses two D3s bodies.  I have corresponded with him a few times and he indicated that 12K is all he needs, and he is certainly not chasing the latest high res incarnations.

In fact, I only recently bought (like you) a mint, very low click D3x.  It is an awesome camera and just reeks of quality.  However, with all of the extensive testing I have done, I can barely tell any difference between shots from this and my D700 (same deal as 'your' D3).  It would be a hard decision, but if I had to choose only one camera it would be the D700.   The slight edge you may get on definition has to be weighed against other factors like, file size, dynamic range and high ISO ability.

I wouldn't bother chasing higher MP in a lesser body, like the D600.  I tested one and compared to the D3, it is a piece of junk.  You will far outweigh any loss of definition with the D3 (compared to D600), with build quality, weather proofing and just the sheer joy of using a camera that reeks of quality.  For me it is a no brainer (particularly for $1,300), grab the D3 and go and enjoy.

Sutto

philipsuttonphotography.com