I didn't watch the whole video, I'd seen enough after about ten minutes. Wow, the utter lack of model details low textures and those über slow LOD pop-in for the sign. Holy crap balls. I don't think it's necessarily I/O related, as in the hardware, as DF had the exact same performance across four NSW units on both internal and external memory and you almost always get a difference internal storage and card.
It's UE4 so maybe it's that issue with UE that you and BRiT were discussing in t'other thread?
I still can't get out how bad it looks. Just..