For 1080 as it stands right now the 770 is a great purchase. I'd only suggest the 780 if you plan to play at higher resolutions or even multiple monitors. Sure, the 780 will stay strong for a few more years since it is the more powerful one. But since you've got the 4GB of Vram you can simply add another for SLI and put those 4GB to use if you also plan to go to a higher res (for textures) or multiple monitors. The 780 will stay stronger for longer but it doesn't justify itself as easily when you can just add another 770 for SLI.