My Cycles preview is really sluggish, even when I reduce the samples. Not sure how to improve this situation besides upgrading my hardware.
Does having multiple GPUs improve the preview speed? I’m aware it speeds up rendering since each GPU handles a tile. But does that work for the preview also?
Sorry if this question has already been asked. When I search ‘multiple GPUs’ on blenderartists I get dozens of threads that don’t answer my question.
honestly good question, been wondering that myself and having 2 GPU’s I never really looked at that.
And to confirm we are talking about changing the shading option in the viewport to Rendered?
I’ll do some testing on my setup and report back soon. Hopefully someone else will beat me to it 
Short answer is a positive YES.
In viewport is accelerated with two cards. I can see in Windows 10 Task Manager that both GPU’s are used and that viewport render time droped by almost 1/2.