You are not "daft" at all. I have not been clear and will be revising the article.
Regarding the curves. Yes, it looks like the D800 in DX Crop Mode will be about equivalent to the D700 in FX and ahead of the D7000. But it's not a cheap decision and waiting to see what the D400 brings might be a reasonable unless you're looking to get into FX and see DX Crop Mode as a big plus.
There is an issue separate from dynamic range regarding the D800. Will the lower diffraction limit have any practical effect on your images? I suspect this will depend significantly on print size (and viewing distance) as well as subject matter.