>We don't know if WB is done using the main imaging sensor or >the 91,000 pixel RGB metering sensor. I don't think it matters >provided both cameras are seeing exactly the same image under >exactly the same light (and they're both using the same lens, >aperture & shutter speed).
Well, not exactly. If (hypothetically) the main sensor on one camera is recording a bit warm, or a bit cold, and if (hypothetically) the wb is done by the AF sensor, and if (hypothetically) it is the same and not customized to the camera, then sensor recording difference will show up on the result.
If the readings are from the imaging sensor, and use the same algorithm in the two cameras (again, hypothetically), you would expect any difference in recording by the sensor to be wiped out by the calculations in "auto" but not in the present temps.