I have two GTX 670s at the moment running in SLI. I've been looking for an upgrade for a while and I have decided that now would be a great time because I've been waiting for the release of GTA V for a long time and I want to run it at maximum settings and frame rates when it comes out. Are the two 670s that I have right now sufficient or should I upgrade to a single 970 or 980. Note that right now, my graphics cards are having trouble running Far Cry 4 on ultra and Advanced Warfare on medium-high, they also make very loud coil whine. If I should upgrade, which brand is the most suitable/best? All replies or recommendations are greatly appreciated.