Nice find, but hefty impedance on those Feg (2.2 Ohm: at least they quote it!). Have emailed Beyer about these: http://europe.beyerdynamic.com/shop/hah/accessories/custom-headset-gear.html. Can't imagine they're any better impedance wise, but seeing as the stock cable on the X1 is 1.8 Ohm you never know. Also both cost a lot, but at least both are ideal if you're lucky to use headphones with detachable cables :)
Also check out these - pretty decent reviews: http://v-moda.com/boompro-microphone/
Yes, the Beyerdynamic is even better. I'll build a headset with the upcoming Custome One Tesla.