They're amazing and can certainly be considered endgame. For me, the HD800s have that 10% extra on the Sundara that make them my personal endgame. Just a bit better soundstage presentation, better mids, less harsh treble.

Are they $1300+ dollars better than Sundara. Absolutely not. Again it's like a 10% improvement. I wouldn't say it's wise to spend $1600 on a single headphone, especially when a $300 Sundara is like 90% as good. But sometimes some of us get caught chasing that dragon lol.