occasional magenta/green blotches

ISO 200 won't help. It's ISO 100 under exposed and developed back up. You lose more control of the tonal range that way.  What If find it's best (applies to all cameras), is to find by spot metering at what point the data will become unrecoverable, then measure in the shot accordingly, and let the areas that you want to burn, burn.

I got pretty good at this with the Olympus e-420, 620, E-3 and Pentax Q.  You can control very well so that you avoid burns where you do not want them. Of course, if you have a really high contrast scene, you will still be losing shadows to noise when you bring them back up if you want them visible and not burn anything.

The DR of ISO 100 and ISO 200 are the same. What changes is how it shifts, so you have more highlight range and less shadow range at ISO 200.  ISO 100 and ISO 200 are one of the same coin, it's just how the camera under exposes and develops back up to shift the total tonal range.

You will not gain more total DR by going to ISO 200, and you do lose more control over how to use the total DR (this again, applies to virtually all cameras that have this shift).  ISO 200 advantage is if you are in a hurry and you want to make sure you don't miss highlights and can't be methodical about watching for the highlights, then you can dial ISO 200 and not be as careful.

But then the shadows won't be as nice but that will depend on the shot.

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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