Base ISO on your D7000 is 100. On the D90, D300s and D3s it's 200. But on the D3x it's 100.
Your D7000 offers very good IQ that rivals the more expensive bodies, even at moderate ISO, and in fact exceeds that of the D300s for example.
As the digital age progresses I believe we're going to see less of a difference in image quality between cameras and in time, perhaps even at the higher ISO's. The seperating factors will, however, remain things like build quality, weather proofing, focus speed and external feature set.