Does the Canon 5D Mark II have banding issues at or near base ISO?
The RAW converter of files sometimes makes all the difference in the world.
What I have seen is a problem with RAW converters interpreting the data correctly.
IMHO the demosaicing of the 5D2 files is a finicky task.
It's a double edge sword extracting every last bit of data, adding sharpness, and avoiding the demosaicing artifacts associated with the bayer pattern and sensor read noise.
Enlarged version and cropped to fit the dang 600 pixel maximum.
In summary be carefull of your settings and RAW converter of choice. Sometimes the manufactures know best...