Anisotropic filtering has to be 2x too, but what’s the value of it in UE4 by default? (and where to change that?)
Got fps counter up yesterday, although I didn’t have time to test it with default scene vs your scene.
Are you referring to Performance Guidelines for Mobile Devices | Unreal Engine Documentation when talking about mobile optimization ? If so, so far the only thing I haven’t done is checking the materials and r.MobileContentScaleFactor. I disabled mobile HDR and post process stuff on camera and in project settings.
I still think virtual IPD is off 
Any idea how to tweak that in UE4 ?