The NEX 5N is better at high ISO's than the A99 :-(

Zeiss 18mm on an e-mount?  Never heard of that, unless you are using the expensive compact prime cine lens?  Are you sure you didn't mean Zeiss set to 18mm?  And if so, would this be the same Zeiss 16-35 that was used on the A99?

Where's the EXIF info? Aperture? Shutterspeed? Focal length?

What were you focusing on?  It almost looks like focus is slightly off between the two.

Were both cameras on a tripod?  Was steadyshot turned off on the A99 if it was on a tripod?

If out of camera JPEG, what were the JPEG settings in the 5N versus the A99?

Keep in mind that for the A99 to match the approximate focal length of the 18mm on the 5N, the A99 would need to be close to 37mm.  So in this case, the Zeiss should be at 35mm.

Also, you can't use the same aperture on both to meet the same depth of field.  For example:  If the 18mm was shot at 2.8 from 6ft away, the Zeiss at 35mm from 6ft away needs to be shot at 7.1 to have about the same depth of field.  This will also effect your shutter speed.

I have a hard time believing the 5N is superior to the A99 at high ISO, even if the A99 loses about .3-.5 stops due to the mirror.  For one, the pixels on the A99 are little over 55% larger than that on the 5N.  Second, with the A99's lower pixel density the image should appear less noisy if pixel peeping on a screen (assuming normalizing was not taken into consideration).  If anything, this just shows the difference in the JPEG compression used between the two cameras. What are the JPEG file sizes for each, out of curiosity?

I would be more curious as to how they compare from RAW.  While I don't want to start a RAW/JPEG debate, I myself wouldn't be buying an A99 to shoot JPEGs.

Sorry for the "20" questions.

--
Paul