That would be an interesting comparison Colin...start with the D700@1.4 and then move on to the 7200
There's no magic when it comes to the laws of physics, but I'd estimate that the sensor in the 7200 has better QE than that in the 700, it's just being compensated for by the larger pixels.
In Greg's example, I'd speculate that Sony is keeping technology (or perhaps smoothing algorithms...) to itself.
Full frame is always going to work out more convenient because of the fewer panels, but it if the aberrations towards the corner are more apparent on FF then you might need to crop more than you'd bargained for.