Really bad editor performance

Because I am working on a scene that has 1,000's of GOs, I have quite a bad time working in the editor.

In my smaller sample scene, I have many tiles all which seems to really slow things down. Zooming the camera in does not improve performance.

I have attached an image that shows how bad my performance really is, just sitting idle, staring at the scene view + game view.

Is there a known solution or work around that can be used to help alleviate my symptoms?
Any help is appreciated.

Unity Version: 2017.4.3f1
CPU: i7-4770K
GPU: GeForce GTX 680 (x2 SLI)
Available Physical Memory: 27.2 GB
Available Virtual Memory: 54.8 GB
OS: Windows 10.0.16299
Unity Installation Medium: Samsung SSD 850 EVO
Project Storage Medium: Samsung SSD 850 EVO

 

According to the screenshot, it seems most time is being spent in GI related systems. Do you use global illumination and checked its settings already?

 

I will check and fiddle with the GI settings.
Sometimes though the performance will improve for seeming random reasons. This is shown in the second image, where GI is not a source of the issue.

 

Mixed Lighting -> Baked Global Illumination.

Info given when turned off says it will use real time, but I want to used baked lighting only in my scene.

Having this turned off, seems to have no effect on my lighting, but using the editor now feels like nice, warm butter running through my fingers.