Bambu Labs has contacted me directly on this issue, and I am told that the actual printing speed relates to the following formula. Speed = Max volumetric speed mm squared/second / ( Layer height * Line width). So it would appear that if the speed settings in your process settings are higher than the results of this formula, the formula takes precedence. In my case for ColorFabb HT filament, 10 / (0.16 * 0.42) = 149mm/s for the outer wall, and 10 / (0.16 * 0.45) = 139mm/s for the inner walls, MAXIMUM speed. That is why the outer walls print faster, and NOT actually at the process settings. Seems like the process layer speeds only take effect as maximum speeds if your volumetric flow rate is sufficient to make them relevant.
UPDATE:
OOPS! Sorry! Got the formula a bit wrong. Should be Speed = Max volumetric speed in mm CUBED/second / ( Layer height * Line width). Apologies!