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).
Pentax K-x vs. Nikon D5000
Pentax K-x: Pentax 50 mm F1.4 lens, Aperture Priority, ISO 200
JPEG Large/Fine, Manual WB, Default Parameters (Bright CI), Self-Timer
Nikon D5000: Nikkor 50 mm F1.4G lens, Aperture Priority, ISO 200
JPEG Large/Fine, Manual WB, Default Parameters, Self-Timer
5.1 MB JPEG (4288 x 2848)
5.2 MB JPEG (4288 x 2848)
Unsurprisingly there is only very little difference between the image output of the Pentax K-x and Nikon D5000 - both cameras are built around the same 12.4 MP Sony sensor. Colors and tones are near identical and only at very close inspection is it visible that the Pentax uses a marginal amount more sharpening at default settings. Even at very large print sizes would the output of these cameras be pretty much indistinguishable.