I didnt do any mesh optimizing, and baked all the textures at 4k. Ran out of texture memory (or w/e its called, cant remember!) as soon as you walked out of the lift lobby. Once the SSR etc was added, good bye.
Also tried doing simpler baking, just individual diffuse textures and then lighting again in UE4. Eventually fell over after 50% of the furniture was added.
It was cool when it worked, but it really would have needed optimization.