Looking for best settings for creating Rift video content

I have asked these questions in a number of different forums but have not got any responses as yet.

I am creating a short Sci-Fi film using CG and Live footage as a stereoscopic 360 clip.

I would love to know the following.

Is there an optimal resolution for video playback to maximise the resolution of the Rift headset for 360?    I have been using H265 with pretty good results at approx 8K by 2K at 50 fps.

Do any video player support 360 audio?   (Using Whirligig, best of the bunch I have used so far).

Would shifting from a 970 GTX to a 1080 improve video playback performance?

Thanks