I understand this can be frustrating. And you have a need to be productive at a decent framerate. I also get you would like to understand why the editor is now performing poorly. I’d like to help you solve your issue. Would you be willing to tell us which experimental features you have enabled? Could you possibly evaluate the performance differences between having those features turned on and off so that epic will have a better understanding of where the problems may have been introduced?
As you know, features change from build to build. It would be nice to know which ones specifically are potentially causing your issue. If none of them have an impact, then there is a problem with the core engine features and this is good information to have to zero in on a solution for you.
Alternatively, have you recently updated your graphics drivers to a beta or legacy version? Do you have any other software that performs slowly after a Windows 10 update perhaps?
I have found that updating my graphics drivers sometimes has adverse affects on my performance in Unreal and I have had numerous occasions where I’ve had to reinstall older graphics drivers to resolve the issue. I aslo know that we have recently helped to improve the DX12 support in UE4 at Microsoft and as a result specific drivers may cause issues with performance with any features that would leverage DX12 since your card doesn’t support DX12 (But neither does mine). But then again i’m not aware of any features that require DX12 as of yet, and the big gain was in performance. But I also am not terribly familiar with the new features of 4.11 (but the folks at Epic are 
)
I checked your dxdiag but i wasn’t able to parse the driver version to the driver versions on nvidia’s website.
More often than not, nvidia recommends not using the latest updated drivers, but only using WHQL.
I am installing the latest drivers now to see if i have any difference in performance.