Look like NVENC encoding speed is TWICE as fast as PASCAL but NEW SDK is required.
1* The video encoder in Turing GPUs has substantially improved quality and performance compared with Pascal. The overall encoding capacity of one NVENC in Turing is comparable to two NVENC’s in Pascal.
** The Video Codec SDK, which exposes new encoder improvements and features of Turing will be released soon. Until then, users can continue to use Video SDK 8.2 on all GPUs.
and
* The version of Video Codec SDK which exposes new decoder improvements and features specific to Turing will be released soon. Until then, developers can continue to use Video Codec SDK 8.2 on all GPUs.