P.S.: Can't upload the raws, I'm on the road....
It's difficult to make a diagnosis w/o the raw files. The point is, that ACR is making automatic "exposure" adjustments depending on the ISO, w/o showing that on the "exposure" slider; this can fake overexposure, or hide underexposure with ISO 400 and 800, or the opposite with ISO 100.
There are two ways to determine in ACR if there was real overexposure:
1. reduce the "exposure" a lot. The right edge of the histogram moves to the left. If the right edge shows a sharp, abrupt end, that is raw clipping.
2. Try to pick WB from the very brightest spots (no matter what color it has). If you can, that spot is not raw clipped. If you pick and there is no change, click once more on the very same spot; the message tells you, that that spot is not suitable, i.e. clipped. Note, that this has nothing to do with the red clipping indication: you can increase the "exposure" and cause clipping indication by ACR, but that is not raw clipping and you still can pick WB on such points. The opposite way: you can eliminate the clipping indication (the red) in ACR by reducing the "exposure", but that does not eliminate the raw clipping.