It wasn't SLI, just some BIOS option I didn't switched properly. I tried again and I've managed to disable only internal nvidia keeping intel working. Interesting results though with 3DMARK Fire Storm With *only* GTX970 working on external monitor connected to GTX970: Score: 7602 / Graphics Score: 9736 / Physics Score: 6210 / Combined Score: 3295 With iGPU and GTX970, external monitor connected to laptop HDMI: Score: 6633 / Graphics Score: 7321 / Physics Score: 6921 / Combined Score: 3755 With iGPU and GTX970, external monitor connected to GTX970 HDMI: Score: 7781 / Graphics Score: 9542 / Physics Score: 6850 / Combined Score: 3570