occasional magenta/green blotches

Just in a different way:

" In contrast, at ISO 200 and 2 stops overexposure, the results are essentially identical to overexposing ISO 100 by one stop. This means that you'll get maximum latitude for overexposure at ISO 200; we'd estimate you can expect to recover at least 1.3 stops above the JPEG clipping point with full colour accuracy. This in turn means that in bright, contrasty conditions we'd recommend using ISO 200 by default."

They aren't saying you get more DR. In fact, they say pretty much what I am saying- you get more highlight range at ISO 200 (note there is no mention of shadows or total DR).

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Raist3d/Ricardo (Photographer, software dev.)- I photograph black cats in coal mines at night...
“The further a society drifts from truth the more it will hate those who speak it.” - George Orwell