I think the urge to label what we're hearing is what does us in. I now try to judge a headphone or any other bit of gear on a one-dimensional scale. How much do I like it? That has the advantage of not really implying some sort of tradeoff or decision. When we get into the "Too much treble, great mids, the soundstage was wide but not deep, bass was full but loose, not fast enough for such-and-such music..." kind of stuff it's no wonder it becomes impossible to make up our minds. Who knows whether "great mids" is more important that "deep soundstage", that probably varies from day to day.
Stick to simple A/B comparisons. Listen to all kinds of music on a K702, give it a good workout. Then listen to a similar mix of music on a HD650. Afterwards simply ask "Which one did I enjoy listening to more". And if you feel the urge to say anything with "but" or "except" in it (i.e. "The K702 was better to listen to but the trebles were harsh") then just slap yourself until you shut up and answer the question. Which one, A or B, '702 or '650, AKG or Senn. Which one?
That makes a lot of sense to me. I would also add, "which one made me forget that I was listening for sound quality..?" That's always a sign of a good headphone. The 650's for me, make you forget about sound quality because nothing jumps out at you, or seems to be taken away. You can listen for hours and hours without going "wow! I really felt that bass" or in contrast "the treble was great but it's wearing me out now.."