The Nighthawk has been scaling a bit on better gear, it's still the same signature tonight but there's some separation improvements. The mids still have hay boxy feeing though, that's due to the semi closed design plus the tuning.
The HD650, this thing is a beast. It just keeps improving. It straight out beat the Mrspeakers Ether I borrowed and it sounded as good at times, as my HE1000.
While the Nighthawk made some improvements the HD650 peed all over it, not even a contest! That speed of the HD650 driver is pretty crazy.
I tried the HD650 on the Dragonfly and the ODAC after and I can see why some people are saying they like the Nighthawk better, I never realised how bad the 650 sound on entry level gear. Grab yourself a good DAC and the 650 will match pretty much anything out there.
The Nighthawk had really impressive bass on everything I tried. The Mojo with the ember on high gain was pretty special.
The HD 650 does sound bad on underpowered gear and definitely does scale a good deal. Don't really agree that the HD 650 scales more than the Nighthawks based on my experience with high-end gear, I just found the Nighthawks easier to make sound good as they are less demanding of amplification and have a much flatter impedance curve. I found the Nighthawks more revealing of the system than the HD 650 imho. Most Senns have rather odd impedance curves, this makes them rather picky of the system as many systems can't power them properly. A good DAC also makes a big difference of course. Tuning of a headphone definitely plays a big role and I get the feeling people consider different things good. I do find it interesting how different peoples opinions on headphones are even on the same gear.