For a (more) level playing field for comparison we also shot our studio scene in RAW mode with each camera and converted it using Adobe Camera RAW. Because Adobe Camera RAW applies different levels of sharpening to different cameras (this confirmed) we had to use the following workflow for these conversions:
Load RAW file into Adobe Camera RAW (Auto mode disabled)
Set Sharpness to 0 (all other settings default)
Open file to Photoshop
Apply an Unsharp mask: 80%, Radius 1.0, Threshold 0
Save as a TIFF (for cropping) and as a JPEG quality 11 for download
This is our standard studio scene comparison shot. Lighting: daylight simulation, >98% CRI. Crops are 100%. Ambient temperature was approximately 22°C (~72°F).
Nikon D90 (RAW) vs. Nikon D80 (RAW)
2.9 MB JPEG (4288 x 2848)
3.6 MB JPEG (3872 x 2592)
With the effects of the camera's JPEG engine removed, the results from the two cameras are much more directly comparable. Despite the greater pixel count of the D90, there's essentially no resolution difference between the two, with the D80 perhaps edging its younger brother in terms of per-pixel sharpness.