JPEG signal to noise ratio
Raw signal to noise ratio
Olympus stated that the E-M1 is calibrated to allow a little more noise to be visible to retain detail and improve image sharpness, and this is likely to be the explanation for the lower signal to noise ratio. However, images don't appear very noisy and there's little in the way of coloured speckling visible.
JPEG dynamic range
The Olympus E-M1 is capable of recording a wide range of tones in a single image at the lower sensitivity settings, and at the higher values it beats the Sony NEX-7 and Fuji X-Pro1 for dynamic range.
Raw dynamic range
While it doesn't quite match the E-M5, a dynamic range in excess of 12EV at ISO 400 is impressive.