Cuda freezing display with heavy kernels

I have an nvidia gtx 960 which I am using for cuda and my display.

Problem is that it can freeze my screen if I run a heavy kernel.

Today I bought a cheaper nvidia card and installed that in my system. It fixed the freezing issue since I was running my display off of it but I did not like that I could not switch to my more powerful card when I was not using cuda.

My BIOS would only let me choose to use pcie cards and not let me pick which one without swapping the cards in their slots.

Now what I am thinking of doing is getting a second gtx 960 and running SLI.

Do you think this will help with the freezing since when I run a cuda kernel only one of the cards will be swamped?

BTW I am running ubuntu 15.04