I spent a few months to find a good upgrade from the HD598. I had tried HE-500, LCD2.2, and Grado GS1000. I had never wanted to try a HD700 after having read the criticism about the sound and the bad measurements. Between those I chose the LCD2, but because a friend's suggestion I got a HD700 from amazon. I just wanted to make sure LCD2 is the best choose on $1000 range headphones but from the first minute I tried the HD700 I found that it’s not as bad as some of the reviews.
After burn-in the headphone for around 40 hours I spent whole a weekend to compare HD700 to LCD2, to me they had a same sound quality with different sound signature, for some genres I preferred HD700 and for some genres, LCD2. Finally I decided to keep the HD700, since it had a same SQ but much more comfortable than LCD2. The HD 700 feels like it weighs almost nothing on my head and the earpads don’t make my ears sweat even after hours of use.
Honestly I didn’t find any 5.5 kHz peak, but maybe a bit around 6.5 kHz. Yes, I found some hot trebles and sibilance in the beginning but after a couple months of listening what I can say according to my ears and impression, most of them have been smoothen out.
The HD700 build quality is not bad at all; it is constructed by high quality plastic with a hint of metal. I don’t have any concern of its long-term durability base on my experience with other plastic made headphones from Sennheiser.
In compare to my HD650, the HD700 has more trebles energy, deeper and more refined bass, wider sound stage, better instrument separation, more revealing and much faster, though the HD650 is more transparent to my ears.