17-55 ef-s + 24-105, or 24-70 2.8?

[thekingb]

I recently upgraded to a 6D and have the 24-105 mounted. I am blown away by what I can capture in low light with an f/4 lens compared to the 7D. It's like I skipped many generations of technology.

But I am definitely keeping the 7D for now for those situations where I need AI servo mode. The 7D is still better in that department. It's also a bit more rugged.

[gbc]

Is AI Servo mode that much worse on the 6D than the 7D? I'd say at least half my photography is concert shots, where there's usually low light or strobes or other quick and extreme lighting changes, and where the subjects tend to move around unpredictably. So the low-light capabilities are the main appeal of the 6D, but if the AF isn't great, especially at the non-center points, I'm starting to think I may be better off sticking with the 7D and waiting for a price drop on the 5D3. Though that leaves me without a general purpose zoom lens.