[_Spook_]

So, status here on:

OpenELEC-Generic.x86_64-6.0-devel-20151215204732-r21604-g17e2400

Problems:
4k files, both x264 and x265 get random HDMI resets
3D files, x264, get random HDMI resets
all other files OK

Sound is in sync after I stopped using passthrough and now use:
Sync Playback to Display: On
Adjust display refresh rate to match video: On Start / Stop

Logs:
http://sprunge.us/BbfK
http://sprunge.us/JQXK
http://sprunge.us/SAid
http://sprunge.us/EOVL

EDIT:
If I turn OFF Adjust display refresh rate to match video the problems further up goes away. But I get flicker issues with video. And had to fix that with setting GUI to 1920x1080p 23.98 FPS. So as long as I don't have videos with other framerate im all good with OK audiosync and NO framedrop/HDMI dropout.