Update 01/10/2017: The UH7700 just got a new update (04.30.77) that added a new 'HDR Game' mode and it greatly upgraded the performance of this TV. As you can see, the input lag in HDR is now at 15.9ms, which is very good, even for the more hardcore gamers out there. Note that input lag under game mode with a 1080p and 4k resolution also got cut by 10ms.
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downloaded the firmware from US site. done testing. huge improvement in input lag s HDR mode in ps4.