Got a raise and a more permanent position at work so I celebrated by finally picking up some Sennheiser HD650s and couldn't be happier. Coming from a pair of Fidelio X1s, although excellent in their own regard, this is a palpable step up in both sound and comfort. Now I just need to get a proper amp...
I also auditioned some HD599s and came away very impressed. I ran both off my Schiit Fulla 1 (so the 650s were not exactly performing at their best), and the 599s came pretty close to the 650s. For someone not interested in getting involved with dacs, amps and all that business, the 599s would be a fantastic allrounder, especially when the price comes down. Compared to the 598s (or rather my memory of having listened to them two years ago), the 599s have more bass, about the same level as the 650s to my ears, and increased clarity. The soundstage was about on par with the 650s in width, but not as tall or deep. Their build quality seemed improved from the 598s too, feeling a bit more solid and "premium".