multiple GPUs

Hello, I have no clue about these things so here my question:
my system is win7/16GB
Now I´m working for 3 years fine with an Nvidia GTX960(4GB) but reach the borderline more and more (crashes, white screens, blue screens...).
I decided to buy the GTX1080Ti(11GB) and increase my RAM to 32GB.
Is it possible to work with both of them and make it sense and will Iray work faster than? If so, will my PC know about two GPUs or have I tick anywhere?
Thanks in advance, Anja
Comments
See attached. Be aware that the GTX960 won't be used for any renders that exceed the 4GB Vram. Also since the 960 is an older generation, has relatively few CUDA cores, relatively low VRAM, you may be better off to have the 960 power the monitor and and not include in the renders, The 1080TI will be so much faster that you will probably not be able to see any improvement with bith GPUs. Finally, Iray may throttle the clock speed on the 1080Ti to match the slower 960.
Many thanks to ebergerly and fastbike1! That is helpful, I will use just the new one if I will get it. I was asking because I've read so often that people use two or more GPUs together.
@ebergerly " Id first check the W10 Reliability History,"
Shouldn't be applicable, @Enchanted April is running Win 7.