The DXO numbers also show the NX1 outperforms all of the D7xxx series in low light performance (slightly in some cases). So, which is supposed to benefit most from BSI: DR or Noise?
That's not my interpretation of the graph. Below is the DXOMark graph comparing the DR of the NX1, the D7000 and the most recent Nikon upgrade, the D7200.
The NX1 appears to have a slight, but probably noticeable DR advantage at ISO 12,800, compared with the much older D7000. That advantage, according to the test results, is 0.45 EV, which would be worth having at base ISO, or even ISO 800. But ISO 12,800?? I would never bother with such degraded images, so for me that's no advantage.
Also, the D7200 whips the NX1, regarding DR, at all ISOs up to and including 12,800. At ISO 6400, the highest ISO I would ever consider using, the D7200 has over a full stop better DR than the NX1. Now
that's what I call significant.
By the way, the DR specification also relates to noise, but noise in the shadows expressed in terms of Exposure Value. The other DXO noise test, SNR 18%, refers to the noise levels in the mid-tones. The performance at 18% grey is approximately the same for all 3 cameras, with the D7200 having an insignificant edge at base ISO.
To get a worthwhile improvement in SNR at 18% it seems one has to increase sensor size to full-frame.