My D7k performs very well. I came to it from much less capable cameras, so the learning curve has been a little long, but the more I practice with it, the smarter it seems to get, especially as I get into video - the main reason I moved to the D7k from a D80.
I'm a little puzzled by the "invest in glass over time" comment, though. Is that suggesting FX glass would work well on the DX camera? Or only if I plan another camera upgrade. (Though I haven't really studied it, the D600 does look inviting. OTOH, I think were I to upgrade from the 7k, I'd make a bigger jump.)