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 D300S vs. Canon EOS 50D
Nikon D300S: Nikkor 50 mm F1.4 G lens, Aperture Priority, ISO 200 (default base), JPEG Large/Fine, Manual WB, Default Parameters (Normal), Self-Timer (with exposure delay), ADL off
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
Canon EOS 50D
5.1 MB JPEG (4288 x 2848)
5.0MB JPEG (4752 x 3168)
The difference between the D300S and the EOS 50D isn't nearly so pronounced, however, with the Nikon showing fractionally lower level of really fine detail but overall producing an image with better contrast and similar levels of sharpness.