I must agree with Philodox there, the HD-650 is no doubt a good phone, definitely the best of the Sennheisers, but it still has that signature Sennheiser darkness to it, which I don't much care for. If I ever were to get a Senn, it would be a 650 (or maybe a 595), but I have to say that the AKG sound appeals much more.
However, they are both very good counterparts to the HF-1. It just depends on what sound signature you like more at this point.
Aditya