Thank you so much for your replies on the durability of these great 'cans!
Yesterday I A/B compared the HD650 with the Q701 and the HD650 are better, IMHO. The sound on the Q701 is still a bit too thin and makes vocals a bit screechy. The soundstage is wider, but not as sharp as on the HD650 as these can convey a sense of location of the various instruments much better. The highs seem equally detailed on both headphones, just more pronounced on the Q701. The Sennheisers are a much more bassy phone (I didn't expect such amount of bass from a "reference class" headphone), but it's very well integrated on the sound spectrum.
All things considered, the Sennheisers sound "higher-end" to me, more refined. And are also easier to drive than the Q701!