Normlly I'd say the decision would be driven by what you shoot and how you shoot it. But first I have to disagree with a few of your thoughts.
I found the D3s to be a significant upgrade over the D3. It has better overall ISO performance and better high ISO performance. It also have sensor cleaning.
I would never consider the D3x. For the same money I'd go straight to the D800. Best dynamic range and color out there. Excellent ISO performance — at the same print size it matches the D3s.
I still have mu D3s. It is built like a tank, it's utterly reliable, and has that wonderful FPS rate. Last year I sold my D300s and replaced it with a D800e (I passed on the D3s to D4 upgrade as I didn't think the benefits met the cost). I still have my lower-pixel machine gun and now have simply the best image-capture body out there with all those pixels to crop.
Jon Kandel A New York City Nikonian and Team Member Please visit my website and critique the images!