for a "travelling street/candid/portrait photographer"? Well, I run around in Venice mostly with the 24-70/2.8 on my D300 (see report here
) and found it very usefull. But you have to remember the crop factor, so to reproduce the same on a FX-body I'd need a 35-105/2.8 lens - and a tack sharp one at that. But unfortunately such a lens does not exist (would be nice to have it stabilized too). The nearest thing is the Nikon AF-S 24-120/4.0 VR, but that is optically not up there with the 24-70/2.8.
So as Dubaiphil has pointed out: on an FX-body you need something longer and a 85mm large aperture prime (like the new 85/1.8G) would be a nice choice.
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
, My Pictures
, My Photography Blog