5D Mark II and Mark III
I compared shots taken under exact the same conditions at various ISO levels.
The subject is a 20cm (about 8") high porcelain, hand painted statue against a neutral grey linnen backdrop.

The lens used was a Canon 50mm F1.4 USM on auto-focus at F8. The only changes were in the shutter speed (variing from 1/4' to 1/1000'). Focal point, subject distance (85cm) and lighting level were constant. Lighting was by two 55W luminescent lamps at 5500K into silver coated umbrellas.

All shots were taken in RAW - neutral and have a 50% sharpening in Adobe RAW Converter. With the exception of the first two shots all crops are at 100%.

Noticeable is the 2.5% increase in sensor size for the Mark III.
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