I too am having difficulties with the D7000. Attached are three photos, all taken using a Nikon f/2.8 70-200mm with the TC-20E III at 400mm with VR off. The initial images were cropped (using Photoshop) to cover approximately the same area for comparison purposes. No other adjustments were made. These were taken under different lighting conditions. All three cameras were set to matrix metering, focused on infinity, WB auto, sharpness normal. For purposes of this post, all three were uploaded at 800 pixels wide.
The quality of the D7000 shot appears inferior to me. Any comments or suggestions would be appreciated.
Camera: D700 with cropped area of 830 x 503 pixels f/7.1, 1/3200 @ ISO 800, NEF = 14,816kb
Camera: D3x with cropped area of 1,183 x 719 pixels f/7.1, 1/2500 @ ISO 800, NEF = 50,008kb