There's still time to edit this baseless comment.
Do the right thing.
Well, I am kinda sorry if it is not with your tastes, but I am the type of person who really likes all HD650, HD700 and HD800, and even HD598, but I would not listen to the same song with all of them. Or the same type of music. I am unable to find that exact post, nor I know to what exactly I should change it.
Generally speaking, I like Sennheiser a lot, but I kind of see HD650, 700 and 800 be for totally different people. Kind of like they have completely different signatures. Not even made for the same purpose. HD650 is like the warmest, most natural, most relaxed headphone I had tried, but still had amazing resolution and details. HD800 was like extremely revealing, amazing huge soundstage. And HD700 was like, extremely detailed, but the sound was neither rolled off at either end, nor over-expressed, it had a smaller soundstage than I expected. Rather, it was like, the perfect headphone for some peculiar types of metal and a few other genera, but I would not see one person having all three, but rather I see everyone choosing one and liking it better than the others. This does not mean that any of them does a bad job, they all are amazing, but extremely different.