It's hard for me to see an advantage of the M8 over the R1 - particularly if the key metric is being unobtrusive. The ability to use the R1 as a waist/chest level viewfinder is, I think is a signficant advantage. It can be perfectly silent, has reasonable noise performance and a pretty decent lens with a reasonable zoom range (at least considering the M8 options).[a href=\"index.php?act=findpost&pid=83032\"][{POST_SNAPBACK}][/a]
There really isn't what you could call a "key metric." I shot Nikons for 30 years before coming to an R-D1 and then an M7, and soon, I hope, an M8. There's just a different method of operation and a feeling about them. One that often isn't mentioned is that with an rf viewfinder, you can "look around" the image -- see stuff outside the framing lines, which allows you to make minute framing changes. Not even the best DSLR finders are as good.
The Leica lenses are sharper and usually faster -- the R1 lens is great for zoom, but, it's a zoom, with all the advantages and disadvantages. Most of my lenses are f1.4, and I also have the f1 50mm which I think would be three stops faster than your R1; it's an amazing experience, if you've trained with film, to take a bright picture in dim light. The other night, with the RD1 set at ISO 800 and the Nocti, I made a shot of an orchid in the light of a single lamp, in the evening, and when I brought it up on my computer, it looked like daylight. It would be an incredible combo for a wedding photographer who works in dimly lit churches.
The cameras are also small. The Leica is somewhat smaller than the R1 and somewhat lighter, I think, although perhaps not with bigger lenses.
I really think the excitement about the M8 isn't so much its capabilities in delivering image quality, which can be matched or exceeded by a 5D, as in its handling characteristics. It's very unobtrusive and quiet, and just about half the frontal size of a 1Ds2, and very unaggressive looking. At the same time, it delivers photos that can be compared to the best IQ out there.
If I were a pro and could only have one camera, it would be a Nikon DSLR. If I could have two, the second would be an M8.
JC