I agree with David. Which is one of the reasons the D300s works so well for you.
I rented a D800 a little while ago and although it's a spaceship of a camera and the files were amazing, it made me realise that I don't need or want one. Apart from being technically OTT, if you're not a studio or landscape type who can take time over changing settings, it's an ergonomic step backwards from its predecessor.
My D700 is a fabulous bit of kit and I bought one because a great many of the other shooters I've worked with and respect rate it so highly. My mate
Simon shoots with exactly the same two cameras you do and despite his predilection for girls in their pants, makes some
fantastic images. Until I can make as much good work as he does, I'm going to try and avoid buying another SLR.
On the other hand, that's not to say I could discount the possibility of a set of Quadras in my future at some point...