Thanks again for the measurements. I'll investigate the driver mishap later, from the graphs it almost looks like it was knocked out of position.

don't worry, the Zu Mobis cable will sort it out. 

Yeah, I'll just use the stock cable on the opposite site to balance it out 

My older black driver, original pads and stock cable HD650:



and CSD (left and right superimposed)



I listen to it like this:



Note the dB scale is 5dB/div and is 'stretched' in vertical sense compared to the usual graphs shown here.
Sounds like the measurements show as well.
It's one of the headphones I will never part with.

I can't do any (relevant) THD measurements as my mic pre-amp is far too noisy which is not important for FR and good enough for CSD above 500Hz.

I like the HD650 mostly because it has about the least amount of distortion of all headphones out there.
In your measurements the HD seems to be below your noise levels as well (maybe the 2nd harmonic is slightly above it).

Perhaps you can make an HD plot without any signals to the headphone and determine your noise floor...
might be a good HD benchmark.