Quote - Another thing which surprised me is that GPU usage has a big impact on the overal UI of the entire system. If you render other apps will be quite sluggish in their UI. It is not a solution for offloading CPU power to the GPU and getting a more responsive system.
I guess that is why some people recommend having three cards in their system with one being inactive in Octane

 

I use two videocards in my system. One is for the attached display device and the other is only for Octane Render. The card for the display is disabled (unchecked) as a Cuda device in the Octane Render program preference settings menu.

By having 2 videocards, one for the display and the other dedicated to Octane Render you will not have a sluggish UI when working with Octane Render or Windows. Another advantage is that all the RAM on the card dedicated for Octane Render will be available for your Octane Render scenes.