If HD650 is your reference i strongly advise you to stay away from planars.
Everyone is flaming the Hifiman build quality but to my experience after owning a HE-400 and a HE-400i and treating them quite harshly sometimes (i'm not the kind to pamper my headphones, i use them, travel with them, even take them hiking) both are still intact.
I'll receive a Sundara tomorrow and will post some impressions here asap. I'm surprised to see no proper reviews of it here actually.
EDIT : I received the Sundara as expected, i was impressed by the shipping box from the Hifiman factory, well padded box with anti moisture bags, and the Sundara product box inside with more padding, my local dealer added another box around with more padding, to damage the headphones it would have needed a truck to drive over it. Well done.
None of the quality control issues i saw mentioned on various websites and youtube videos, everything is fine with my Sundara, headband, pads, all fine.
Now time for a listen....