So now that ES3.1 can be used out of the box and my new PC can handle ASTC compression much better than my old rig, I gave ES3.1 + ASTC a spin, for Gear VR (using my S6).
Turned out ES3.1 + ASTC renders much slower than ES2 + ETC2. ~20 fps difference at times. Is it by design or is it something that is still being worked on as far as optimization go?