Here they are.
I just got my HD650s delivered today for 320$ from J&R. First thing to notice - classy looking box, holding a classy product.
These headphones look beautiful. The headband is different from the 595s, the earpads look kinda the same. First thing I did was to put them on my head, even before plugging them in. The clamping force is stronger than that on the 595s, but still the overall comfort is way better, as the ear isn't touching any part of the phones in an irritating way. So far so good.
Then came the real test - the sound. I use the phones plugged into my Xonar Essence STX Headphone Out, with default opamps (some new are coming this way). After some testing without any burn-in my impression is that the greatest thing about these headphones is the detail. They are times more revealing than the 595s (most comparisons will be with these phones, as they are the only other mid-hi end pair I have). This can work in both ways, as if the recording is good and in lossless quality, the cans will also sound that way, but if it is a low-bitrate mp3, well, you know. The overall sound signature is similar to the other Senns, but it improves all weaknesses they had - the bass is not anemic anymore, it is powerful, yet completely under control (unlike say 212 Pros), the mids are sweet and quick, and the highs are definitely present without being harsh.
The phones are a little more laidback than the 595s, but are still suitable for all kinds of music, including metal and rock (listening to Dark Tranquility as I write this). I can only assume the Xonar is driving them properly, as I do not hear any lacking energy or punch over the whole spectrum. So far I feel there is no such thing as the Sennheiser Veil™, this might change with burn-in though. I can only hope they will change for the better. I plan on listening to them during the day, and leaving them to burn in in the nights.
So yeah, another satisfied HD650 user.