This is our standard studio scene comparison shot taken from exactly the same tripod position. Lighting: daylight simulation, >98% CRI. Crops are 100%. Ambient temperature was approximately 22°C (~72°F).
Nikon D90 vs. Nikon D300
Nikon D90: Nikkor 50 mm F1.8 lens, Aperture Priority, ISO 200
JPEG Large/Fine, Manual WB, Default Parameters (Standard), Active D-Lighting off) Self-Timer (with delayed exposure)
This is a comparison that does show something interesting, however. The processing settings from the D90 and D300 can be swapped between cameras, suggesting the output intent is the same. Yet, for all the similarities in publically announced sensor specifications and consistent color rendering, there are clear differences in per-pixel-sharpness and contrast. Both are shot with the same lens but no amount of re-shooting could get the D90 to match the D300's output.