I have a GRD II and I would echo Rick Waldrup's comment wrt it being the perfect street shooter - I would opt for the GRD II on the street over any Leica (ok.. MAYBE the IIIc/f.. MAYBE). And that is because of a few things:
1) Ergonomics - incredible on this small camera - and will get better on GRD III with the ability of another function button
2) Size - pocketable - and the only decent pocketable (literally) cam that does RAW imho.
3) Lens - even at f2.4, the 28mm is ample and in Snap mode is a very good way of shooting street - I can only imagine the III being even better.
With respect to B&W imaging - noise is not grain - period - never has been, never will be. Noise from digital images, no matter how much it may try to emulate grain, has a certain pattern, imho, to it while grain is, I believe, far more random in nature and hence the reason why it's more "aesthetically pleasing" versus "noise".
That said, the GRD II produces nice files which, if converted properly to B&W, can attain a quality CLOSE TO grain (not quite exactly like grain though).
If the GRD III has better High ISO qualities (ISO 800 and, I hope, ISO 1600) then I am just dying to see a review and then, eventually, to snag one of these cameras 🙂
The one advantage that these smaller (some would say tiny) sensors do have over larger sensors is the ability to hand hold the camera at lower 'shutter speeds'. If done properly, you can hand hold the GRD II down to well below 1/15 second and not have "camera shake" - motion blur.. ya.. but camera shake, not so much.. 😀
Cheers,
Dave