A99 tested on DXO - score: 89

Looking at the curves for both these cameras, they're pretty much on top of each other, and about 1/3-1/2 a stop from the NEX-7. This is in line with what you'd expect (since the pellicle mirror causes approximately that amount of light loss).

This is a myth. The NEX-6's sensor performs similarly to the the NEX-5N's, which is more or less identical to the NEX-7's at high ISO when resampled to the same resolution.

http://www.dpreview.com/reviews/sonynex7/22

"The inevitable conclusion from this is that, if you compare images as a whole rather than at the pixel level, the NEX-7's low light, high ISO performance is essentially a match for the NEX-5N's."

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"The only thing that gets in the way of a really good photograph, is the camera"
Norman Parkinson