GTX 690 and MAC OS Sierra not working well...

So, to clear off some of the questions which may come:
How did u shove a 690 in a Mac? -Hackintosh
Blender version? -2.78c. I m not sure if it does this in the other versions since I used that new node thing, and I don t want to remap each and every material :confused:
Now, the thing is that whenever I try to render something or use viewport with that live rendering, it crashes by sayng that there is no more VRam left
Why I am so confused? It should be simple, upgrade GPU.
Not so fast. First of all, Blender says it s using 700-1Gb of VRam for the render, the 690 is made with 2x680 with 2gb each. Now I know that they use a memory pool, but they render as two separate gpus, not as a single one.
https://www.dropbox.com/s/v2e6us2tbbzm5vu/Screen%20Shot%202017-08-12%20at%2002.27.24.png?dl=0 - the link to a pic with the cuda error
https://www.dropbox.com/s/dx28kpyelpoe9qj/Screen%20Shot%202017-08-12%20at%2002.25.14.png?dl=0 - link to pic with system specs