Build runs slowly, editor game view fine

I'm putting together a scene in Unity 5 (Personal). I'm using Deferred lighting in a Linear color space, mainly PBR materials. I've made LOD versions for all the props with a high poly count, and am using cube collision for the entire level.

The places where I am spending a lot of power are the lights and shadows which are all realtime - I can probably scale this back a bit, but I do need mostly live shadows for this scene.

The scene editor runs perfectly smoothly, and the game view runs at 60fps solid (85-95 with no vsync). I have also previously had the build with this model, the collision and all of the lights running at 85 - 95 fps even in the build.

However, current builds are running at around 30-40 fps. The output_log shows no exceptions or problems and I'm not outputting anything into the console at runtime. I've simply created and added some new props, shaders and materials into the scene, and then when I noticed builds were running slowly, removed them again - however the low frame rates remain.

What is interesting is that this 30-40 fps remains even when I significantly change the quality settings. Dropping the resolution from 1920x1080 to 1280x720 makes no difference. I've added buttons to turn off all the screen effects, disable half the lights, turn the shadows from soft to hard etc. - no significant difference. Even changing the quality preset all the way down to Simple makes no difference. Fast however runs at around 120 fps.

Does anyone have any idea what might be causing this, or any suggestions on how to isolate the problem?

output_log.txt

 Initialize engine version: 5.2.1f1 (44735ea161b3)
 GfxDevice: creating device client; threaded=1
 Direct3D:
     Version:  Direct3D 11.0 [level 11.0]
     Renderer: NVIDIA GeForce GTX 780 Ti  (ID=0x100a)
     Vendor:   NVIDIA
     VRAM:     3013 MB
 Begin MonoManager ReloadAssembly
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\UnityEngine.dll (this message is harmless)
 Loading F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\UnityEngine.dll into Unity Child Domain
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\Assembly-CSharp-firstpass.dll (this message is harmless)
 Loading F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\Assembly-CSharp-firstpass.dll into Unity Child Domain
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\Assembly-CSharp.dll (this message is harmless)
 Loading F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\Assembly-CSharp.dll into Unity Child Domain
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\UnityEngine.UI.dll (this message is harmless)
 Loading F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\UnityEngine.UI.dll into Unity Child Domain
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\UnityEngine.Networking.dll (this message is harmless)
 Loading F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\UnityEngine.Networking.dll into Unity Child Domain
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\System.Core.dll (this message is harmless)
 - Completed reload, in  0.096 seconds
 desktop: 1920x1080 60Hz; virtual: 5760x1080 at 0,0
 <RI> Initializing input.
 
 <RI> Input initialized.
 
 <RI> Initialized touch support.
 
 Platform assembly: F:\Projects\Code\Unity\Pub Demo\Build\Pub Demo_Data\Managed\System.dll (this message is harmless)
 Setting up 2 worker threads for Enlighten.
   Thread -> id: 18f4 -> priority: 1 
   Thread -> id: 20f4 -> priority: 1