Oh, regarding the firmware updates. They have definitely been an improvement. The things I like most are the deeper frame buffer, which when you use the highest speed CF cards, can easily reach 35 continuous frames, if not more. Something else that I noticed with the updated firmware was much improved live-view contrast-detect AF. Previously that was fairly slow. It always locked well when it locked, but often it was just to slow to really use. I had to use that a few times recently, and it is much faster than it was. I use that for focusing on the moon as well, which can be very difficult when the frame is shaking. Now that it is faster, I have found that I can get clear focus on the moon without having to do it manually.
The faster movement when chimping is nice, but I wouldn't call it critical. I never really had any serious complaints about the speed of that before, but then again, I'm not a huge chimper. I tend to look at the eye, and if that's good, I call it good. I think there were some other review features added, like the ability to rate photos, and some in-camera editing. I've never used those features really, so I can't comment much on them.
I think it would help if you offered a bit more on your goals.
I own the 7D now, and I think it is an excellent camera. It's sweet spot is between ISO 400 and ISO 1600, however it performs quite well at ISO 100-200 if you don't expect to be lifting shadows by more than a few stops. Above ISO 1600, its performance really starts to drop off, so wouldn't call it a particularly good low-light performer.
I say that, as the only real bit of information I have about your goals was the comment you made about loving the low light performance of the 6D. There is at least a stop, probably more like two stops difference between the 7D and the 6D when it comes to low light (high ISO) performance. You could probably comfortably use ISO 6400 with the 6D. You would likely rarely be able to use ISO 3200 with the 7D. If that difference matters a lot to you, then I would really go for the 7D.
I own both a 6D and 7D and would put the useable ISO at 3200 and 800 respectively. Beyond 800 the noise on the 7D gets to be excessive in my opinion.
I would say the 7D is good beyond ISO 800. The majority of the work on my site (linked in my original answer) is at ISO's higher than 800. I would say the most common ISO setting I use is 1250, and the next most common is ISO 1600, with ISO 1000 and 800 coming in last. I also have too many shots at ISO's as high as 3200. My most recent post with photos of a rather fat American Coot were almost all shot at ISO 3200. I applied a moderate amount of NR, and a little bit of that noise can be seen in those photos, but for the most part...they were more than good enough for posting online. Some could probably be printed at native size (which is probably between 11x16 to 13x19).
The way Canon ISO works, where multiple forms of amplification are used for very high ISO, does not kick in on the 7D until ISO 3200. That is why ISOs 2000, 2500, 3200, 4000, 5000, and 6400 all look very poor, because there is a downstream amplifier between the sensor and the ADC performing the final two stops of signal amplification, and that is only marginally better than a simple digital boost (which is what ISO 12800 is over ISO 6400.) I think ISO up to 1600 is quite good, certainly acceptable, especially if you can really fill the frame with your subject. If you are heavily cropping, then noise at ISO 400 can be quite bad...but that is more of a problem of using the wrong lens than really a problem with noise.
