occasional magenta/green blotches

If you use ISO 200 you can easily shoot +0.7 exp and not lose highlights, since you can recover almost two stops.  So it's pretty safe to do so, using normal judgement as to when to increase or reduce that as a baseline.

If you don't need the DR you can back off to ISO 100 to improve noise.  Then you have to care more about overexposure.

With ISO 200 + overexposure you get more random noise (skies are slightly noisier for example), but fewer blotchy kinds of artifacts (especially because you are filling shadows a bit at time of exposure and not having to bring them up from base exposure as much).

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---> Kendall
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