Adam - First, on the M10-D, I assume it has the same sensor and processing engine as the M10: for me, the M10 blows highlights much more easily than the M9 and the MM; much too easily, particularly on higher-contrast lenses like the new Summaron-M 1:56/28. Generally, I have to underexpose 0.7–2.0 stops, or even more, and raise the shadows significantly in post. Børge has referred to this and "adan", on LUF, has referred to this as the "weird sensitometry of the M10". Have you found this to be an issue with the M10-D?
On the removal of the flash in the GRIII, I found this regrettable as well; but, ultimately, figured that, if the low light capability camera is fine to ISO 6400, as is likely, it should not pose a problem for me. But low light is really dull parkas nothing but flash can enliven an image — is this why you're thinking the lack of flash on the GRIII would limit it to daylight shooting for you?
I arrived in Paris last night, and learned that there is a general strike expected on Tuesday. I was expecting to go fo a camera store that is likely have received one that would be held for me. If Paris public transport is on strike — they don't announce in advance — Paris traffic will be bad, as people bring their own cars into the city, and taxis will be hard to find. I don't mind having to wait a few days, and shall post some images and comments on the GR III on the Ricoh thread here.