I'd go with a 7D. Excellent low-light performer, great focus system, does video (if you ever feel the need to) and is a 1.6 crop, giving you twice as many uses for each lens.
See, in my testing, I didn't find the 7D to be that great of a low light performer. When compared to my 5D it was just 'OK'. Just because Canon says it is so doesn't make it so
. And just because it can shoot at ISO 6400, doesn't mean it's something I want to use as a full page spread in a wedding album.
IMHO, Canon has yet to make a cropper that produces a file that is even close to one of their FF bodies. Not that the file is everything. People have been creating amazing work with cropped bodies since the D30. But if you are used to the amazing files that the 5D2 produces, you may be a tiny bit let down by the 7D. Even as you are wowed by all of the great features that Canon finally decided to pack in (features that were in the D80 I purchased during my brief dalliance with Nikon 5 years ago...if the files from that camera didn't suck, I would be a Nikon shooter now...and now that Nikon's files have caught up, it doesn't make financial sense for me to switch. Grrrrrrrr).
In fact (and I know this is sacrilege), my 5D2 isn't all that much better at high ISO's than my 5D. Canon did a little trickery when they came out with the 5D2 and fudged the light gathering performance of the ISOs. So for the exact same scene, I can put in the same settings on my 5dc and my 5d2 and the 5D2 will give me about 2/3 stop brighter a file. So ISO3200 on my 5Dc is almost ISO6400 on my 5D2. And the noise at ISO 6400 on the 5D2 looks about the same as the noise at ISO 3200 on my 5Dc. Impressive that they were able to do that while increasing the pixel count, but it's not the revolutionary step up that they claim.



