Hi, i have a laptop with Geforce 860M 2GB VRAM, and i want to buy a 4k display for it, so i have a larger screen for my desk. But many people on other forums says that 2GB of VRAM is not enough to run a 4K display, but how can the new iMac run 5K with only 2GB VRAM?? (5K is almost double as mant pixels as the 4K)