Source:
http://www.theverge.com/2015/9/2/923...emium-specs-4k,
http://www.sonymobile.com/global-en/...ia-z5-premium/
Sony revealed 3 new phones for the Z5 lineup today: Z5 compact, Z5, and Z5 premium. Z5 premium is the world's first 4k display smartphone with a resolution of 3840 x 2160 pixels. This is in contrast with other flagships with QHD (2560 x 1440) or FHD (1920 x 1080) resolution.
Notable upgrades from Z3 include the 5.5" 4k display on the Z5 premium (with a whooping 806 pixels per inch), 23 MP rear camera with the newest Sony sensor (0.03s autofocus), 5 MP front camera, finger print scanner integrated with the home button, 3430 mAh battery,and Octacore Snapdragon 810 processor.
Retained features include: 2 day battery life, IP68 water proof rating, micro SD support, Digital noise cancelling and quick charging.
For pixel density comparison:
Xperia Z5 premium - 806 ppi
Samsung Galaxy S6/S6 edge - 574 ppi
HTC One M9+ - 565 ppi
LG G4 - 538 ppi
Nexus 6 - 493 ppi
Iphone 6 plus - 401 ppi
That silver unit with the glossy back

. I will upgrade my phone soon and if Iphone 6s announcement is lackluster, I'll be picking Z5 for sure.