Compared to...

Studio scene comparison (JPEG) vs 8 megapixels

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 400D (Rebel XTi) vs. EOS 350D (Rebel XT)
10 MP vs. 8 MP

Camera settings:

• Canon EOS 400D: Canon EF 50 mm F1.4 lens, Aperture Priority, ISO 100
  JPEG Large/Fine, Manual WB, Default Parameters (Standard PS), Self-Timer (+MLU)
   
• Canon EOS 350D: Canon EF 50 mm F1.4 lens, Aperture Priority, ISO 100
  JPEG Large/Fine, Manual WB, Default Parameters (Standard PS), Self-Timer (+MLU)

Canon EOS 400D (10 MP)	Canon EOS 350D (8 MP)
3,351 KB (3888 x 2592)	2,882 KB JPEG (3456 x 2304)

There's really no advantage in moving from eight to ten megapixels, the additional 432 horizontal pixels and 288 vertical pixels produce no more detail that can be seen. Indeed if anything the eight megapixel (EOS 350D) image looks slightly sharper 'per pixel' than the ten megapixel image from the EOS 400D.