Johann Espiritu
Lawyer / Ninja
Here's a sample M8 image, converted to BW in Alien Skin Exposure. It has a great film-like quality to it:

Slumber Party by The Johann Espiritu™, on Flickr

Slumber Party by The Johann Espiritu™, on Flickr










Coming from an M3, you will be disappointed with any digital Leica, even the M240 - build quality is nowhere near as good, and unlike a smooth and refined film Leica, they're pretty loud and clunky. The larger size is very noticeable if you shoot it alongside a film M as well.
I owned a M8.2.
Sure it has some quirks, but they never bothered me. And once you get beyond the niggles, it really is an amazing camera. I loved the pixel sharpness and the color I got from it. And when it gets dark switch to black/white at 640 iso. Sure, it's not much, but plenty of film users make do with less. Somehow people seem to think available light photography only started when iso 12800 sensors were made...
Anyway, I loved my M8.2.
I don't know how significant the difference is in practice, but IIRC M8 is rated at 2 fps for 10 shots and M9 at 2 fps for 8 shots.PThe buffer is small, but for the small files it kind of works. This was one reason why I never upgraded to the M9, I just never believed the electronics would be good enough for the much bigger sensor (i.e. file size.)
If you hold the shutter button down in S mode the camera will take 12 exposures (M9 8) at 2fps and then settle down to approx 1 image per 2 seconds ad infinitum, well, until your card is full. As soon as one image is transferred from the full buffer it will accept the next one.I don't know how significant the difference is in practice, but IIRC M8 is rated at 2 fps for 10 shots and M9 at 2 fps for 8 shots.
I did perform two tests with my M8 using a class 2 SD card recently. The first one simulated quick shooting for 15 seconds. The camera achieved 13 exposures, which is the number of exposures I tried to make in that time. No issues with responsiveness. In the second test, I tried continuous shooting for 1 minute. The camera achieved a total of 32 exposures. The first 12 exposures were fairly fast (more or less 2 fps), but after that the camera complained about "data transfer" before allowing each following exposure. These are not impressive results, but they have been good enough for my needs so far. The M9 can be expected to be a bit more sluggish.