All consumer '4K' TV's are UHD 3840 pixels wide.
True 4K is 4096 pixels wide.
Virtually indistinguishable to the average eye so some manufacturers just list them as 4K anyway.
BBC Iplayer will be launching a 4K stream shortly. Possibly before Christmas, if not then early next year. (Selected programmes..including most likely Planet Earth 2)
Its got a 4* rating from What Hi-fi http://www.whathifi.com/sony/kd-43x8305c/review
also a video review by AVForums here...