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).
Canon EOS 50D vs. Nikon D300D
Canon EOS 50D: Canon EF 50 mm F1.4 lens, Aperture Priority, ISO 100
JPEG Large/Fine, Manual WB, Default Parameters (Standard), Self-Timer (with MLU), ALO disabled
Nikon D300: Nikkor 50 mm F1.4 lens, Aperture Priority, ISO 200
JPEG Large/Fine, Manual WB, Default Parameters (Normal), Self-Timer
Canon EOS 50D
4.4 MB JPEG (4752 x 3168)
4.4 MB JPEG (4288 x 2848)
The EOS 50D has a three megapixel advantage over the D300 but again this does not translate into a larger amount of detail. In fact the D300 actually manages eke out a little more detail in some areas of the image. To be fair this is helped by a little bit of extra sharpening and, while it doesn't reveal any discernible extra detail, the 50D responds well to a mild unsharp mask as well. Overall however there's not a huge amount between these two cameras and certainly in print it would be very difficult to pick a clear winner.