This not an easy question to answer as there are lots of variables to take into account, ie your own hearing, your set up, what you listen to etc, imo the 770's seem to divide opinion a bit more than the 1770, the consensus seems to be that the 1770 is a step up in audio quality but is as you say more expensive, as I mentioned in a post earlier the 770 is brighter in the highs, the bass goes deep but is just a touch loose, mids are detailed but slightly recessed, the basic sound of the 1770 is similar ie v shaped but smoother highs and a more detailed and overall more refined sound compared to the 770, what is it that you like and dislike about the 650?, maybe going on reviews, opinions of both phones you can come to a conclusion as to which offers you more of the sound you are looking for compared to the 650, another way of course would just be to buy the 770, keep it for a while and then get the 1770 but of course that will mean you spending more money, if you can't try them out then it is ultimately it is a leap of faith.