Nah, the HD650s are going nowhere. I'm actually enjoying the sound of the K702s more and more lately, the removal of the port stickers adds a nice bit of grunt to the bass and I add another 3db via the MusicBee Equaliser. The peaks are smoothed over somewhat by gently rolling off the highs via the EQ and the overall result is much, much better than the original sound.
I guess if I was to upgrade I would be looking at upgrading the AKGs, something that would give me great detail, good, tight bass - maybe the K712 would fit the bill or maybe I should just get the gel pads for the K702, I don't know