Going back to the playground linked in my last reply, I get 12 fps with a 10x10x10 cube. I comment out lines 181-189. This removes the 1000 physics impostors for all the cubes in the cube. I get 40 fps when looking around, 50 when still. and 60 when looking away. Finding a solution to add and remove physics impostors might work. Only the cubes nearest the player should have physics impostors.
Oh, and the 10x10x10 cube with freezeActiveMeshes didn’t help much. I added two functions, freeze and unfreeze. freeze was called when not moving the camera and when not pressing a key(moving around). unfreeze was called when moving and looking around. I noticed the cubes disappearing and reappearing, and I don’t think that it would be a good long term solution.