These are interesting times what with the D400 and possible 24 mp dx sensor rumor. I don't understand how that sensor could be good at low light, but am keeping an open mind.
As an owner of D200 (sold) and D300 (still have but will sell soon) I agree with your assessments of those two sensors. My main cameras currently are the D700 and D7000. For all the things the D7K does well, it is still not near to what the D700 delivers in low light.
Now mind you if the D800 does as well in low light as the D700, plus delivers additional benefits, the D800 should be a real winner (and the D700 will remain one).