Hi Carolyn,
I got my R-D1 about three months ago and the M8 about a month ago. I'm still putting the M8 through its paces, but I'm really not convinced its worth the money over the R-D1 if money is a consideration for you. Obviously the best approach is to own both. 😀
First and foremost, the viewfinder on the M8 is clearly superior to the R-D1. The longer rangefinder base makes focusing just easier and more accurate. You also get framelines so can use lenses from 25 through 90, while the R-D1 is limited to just 28, 35 and 50. 25 on the M8 is also fairly significantly wider than 28 on the R-D1 due to the difference in crop. But other than that, I don't find there's that big of a difference between 1.3x and 1.5x crop.
The R-D1 rangefinder has its strengths -- it does the job and I find I can focus just fine with the shallow depth of field of the 35mm f/1.2 wide open. It also is nice and bright (brighter than the M8's) and has the 1x magnification, if that's important to you. But when it comes down to it, in my opinion the M8's rangefinder is just clearly a class ahead.
The M8 also has a much deeper buffer if you're shooting in RAW. The R-D1 can shoot 3 shots in quick succession before you have to wait for the buffer to clear. The M8 can do more. I don't know the exact number as I don't often hit the limit on the M8 while it's quite easy to do so on the R-D1.
Also while the R-D1 produces extremely excellent images, the M8 once in a while (it's not always every shot) just gives you an image that is stunning in its "3d" feeling. It's like I can feel the texture on someone's skin on some images. I think the R-D1 fails to get this in part because it has a fairly aggressive anti-aliasing filter on it, as well as the higher resolution on the M8. You can get a lot of sharpness back with proper sharpening on the R-D1 to overcome that filter, and it does sharpen up very well, but you do lose real detail because of the filter.
But honestly this isn't a deciding factor for me. I guess it's because it only happens once in a while, under certain conditions. I think in the hands of a good photographer, they would be getting this impact from the M8 more often. But I guess for me getting uber sharp photos isn't the point for me. It is nice when it happens, though.
The other factors are less clear.
10 megapixels versus 6 megapixels -- really that for me just depends on whether you crop (I don't much) or print large. To my eyes, the Epson is most excellent up to 8 x 12 and I think it enlarges quite nicely at 13 x 17. I don't print larger than that. At 13 x 17 the resolution advantage of the M8 is there but in my mind marginal. If you print larger, I would presume the M8 does pull ahead. Maybe, depending on how demanding you or your clients are.
But this is assuming you're at low ISO on the M8. The noise on the M8 is interesting to me. I actually like grainy images, but from a pure resolution standpoint, I'm not sure where I stand on which I like better between the R-D1 and M8. When I upgraded my Canon 300D to 400D, I found the 400D had more noise at higher ISO, but it also had more detail, and overall I found high ISO on the 400D to be more workable. But I can't say the same for a R-D1 and M8 comparison.
The M8 just has more noise such that I'd rather have images at lower resolution on the ISO800 on the R-D1 than the higher resolution ISO640 on the M8. For me it's a fairly even trade-off so far, but right now I prefer the R-D1 (I shoot a lot at ISO800) but it's also early for me to really say.
Where the R-D1 is superior for me is in its ergonomics. The M8 does not feel good in my hands without its protective case. With it's protective case it's a bit clunky, but grippable. The R-D1 fits my hands perfectly.
I hate having to turn on the LCD to see what my ISO is at. It's nice to have it on the shutter speed dial and having everything at a glance due to the dials. The shutter speed indicator on the R-D1 is better. The M8 you have to read the number. The R-D1 tells you its metering because if the red number is on the leftside of the viewfinder it's slow, if it's on the right, it's fast. You intuitively see the position, not read the number.
Having said that though, the M8 is well-thought out with its shooting menu system.
I really like the winder on the R-D1. I don't like it when I feel I'm waiting for the shutter to recock. The motor in the M8 is faster than my thumb, but it's still a disconnect with the process of shooting photos. On the R-D1, it's just me, controlling the machine, to take the image. On the M8, I'm relying on the machine instead of it being an extension of me.
I think the one thing that's really kept me from bonding with the M8 as I have with the R-D1 is that I know how expensive it is. I don't feel comfortable just tossing it over my shoulder when going out. I worry about dropping it or banging it in a way I don't about the R-D1. If I bring the M8 out to say a restaurant with friends, I worry about having it on the table (spills), but don't quite want to just put it under my chair. Not because it can't take a beating, but because the M8 is a luxury item while the R-D1 is just a camera (a camera I happen to love) to me. The R-D1 just goes under my chair and if I happen to bang it about, it can take it and I don't worry about it.
Anyhow, this is getting pretty long, and I'm still kind of feeling my way about... guess I've been thinking a lot about the R-D1 versus M8 recently. 😀
Best regards,
-Jason