Thanks for your impression :) One quick question, do they maintain the unbelievable comfort I've only encountered with Beyer's headphones? I'm going to guess it just gets better once you spend a grand on 'em, but it bears making sure rather than assuming, if you don't mind my asking.
In my opinion and assuming that your amp is up to the job, the T1 is pretty much exactly what you're looking for. I owned the HD650, K702 and DT880 when I bought the T1... I sold the other three within a few months for lack of use.
...has excellent detail and soundstage, but not the exaggerated detail and soundstage of the K701.
...has bass quantity that approaches (but is not quite equal to) the DT-990, but with much better bass quality and greater depth.
...sounds more like the HD650 than the HD800 sounds like the HD650, but is an improvement in every way.