I have a GTX 1060 6GB in my current build, and I also have a GTX 960 2GB in storage. I was wondering if I got one of these bad boys, and got both of my GPUs in one build (Not SLI or CrossFire, just in the same system.) Would I be able to use both GPUs for rendering simutaneously? I don't care if this means haveing them both render seperate tiles in one instance of blender, or rendering seperate frames in two instances. I'm using cycles for everything I do.
You can, as long they are from the same brand (AMD, or NVidia) you should be able to use them simultaneously to render in Blender Cycles.
If you keep them out of any proprietary GPU pairing technologies setup like non-SLI or Crossfire and the operating system detects them as two discrete graphics cards, Blender should be able to see them as discreet GPUs in the user preferences.
This will virtually linearly decreasing render times proportionally to each additional compute device performance, as opposed to pairing technologies which have significant performance penalties and lose efficiency with each additional GPU.
You can then prior to rendering select which one to use, or both simultaneously, if you want. You can also have each instance of Blender use its own GPU independently, although you will likely experience performance decreases caused by bottlenecks anywhere else in your system.