It also depends on your assets (static and skeletal meshes, texture sizes), models need to be optimized, some models have a very high poly count (vertices), and thus require more resources. Another thing, you can instance meshes, for instance the foliage painting tool lets you place the same foliage mesh, with little additional resource requirements. Then you can create so called HLODs (grouping of static meshes), you can also use the developer tool, merge meshes, to reduce draw calls further. If you use large landscapes it is recommended to add streaming levels, loaded at runtime with the level streaming volume, that way the initial loading can be reduced. Cull volumes let you remove drawing of actors at runtime, depending on the player distance.
Static, especially dynamic lights can use up a lot of performance, lights can be tweaked (reduce cull radius, intensity etc.).
UE4 handles polygons very well, you shouldn’t see any performance dip due to that unless you’re going into the beyond excessive count. It could be dynamic lights, though that shouldn’t tank your fps that much either especially if you’re only using one. From the looks of the scene it seems rather simple. How is the material complexity, what sort of post processing effects are you using and what is the engine scalability set to?
The scene itself is pretty small and simple. The image is just a small part, it consists of a hallways and a couple rooms branching out. The rooms are lit by fire and torch. The materials aren’t that complicated. There is one substance material(for the circular structure-beam), the others are just simple textures, nothing complicated done to them. I am not using post processing effects. My material quality is HIGH and engine scalability is set to EPIC. There are 11 point lights in the scene, each with UE4’s default fire particle.
Perhaps a 770 can’t handle the Epic scalability. I don’t know what else it could be, from the sounds of it the scene is fairly simple. One last thing, I assume you’ve been keeping your gfx drivers up to date?