@Atazhaia I looked at a mulitple gpu when I upgraded to the first PCI-E cards. A second card and the better PSU needed pushes the cost near to what a newer mid-range card that would perform. It ends up swings and roundabouts.
The newest Titan card can render most of the latest games at 4K at "Ultra" or there abouts. Most of the performance issues I have with games is that they simply haven't be optimised on the PC. Dishourned 2 looks a bit better than the first game but the newer engine is much slower on the same hardware (Dishourned 1 worked fine on my old 512mb GPU because even though it was an Unreal 3 engine game it looked more like a Unreal 2.5 engine game and the art style makes up for the looks).