HowTo? Determine whether highlights blown in ETTR RAW file? Need to "zero" all ACR settings?

Since the OP, I've become aware of the RawDigger utility, which seems to display actual 14-bit values from my Canon 5dm2 sensor.  I'm still a RawDigger newbie, and am unclear how to intrepret the values it shows.

I did a 1/3rd stop progression of images from a GMB-like Datacolor SyderCheckr + SypderCube  from under-exposed to over-exposed (increasing the exposure time). RawDigger seems to indicate that the pair of Green channels are being blown / over-exposed sooner than I would expect from LCD blinkies, but that may reflect ignorance on my part. I've posted a question to the RawDigger forum.