There is a system (or tool) for occlusion culling? CryEngine had a system for this, now is automatic. UE4 has some similar to this?
As test, I put a forrest of SpeedTrees on a 8kx8k landscape, and with my Specs (Dual GTX660 TI 3GB + 32Gb ram + i7) I have a poor FPS on playing on viewport. Something around 15 FPS. This is very ugly. When scene is completly finished, maybe we have a 8 FPS.
PS.: LPV + Fully Dynamic light.