The 6700 is still a great gaming CPU, but that matters even less at 1440p resolution. When you move up in resolution, the bottleneck moves from the CPU to the GPU. This is why when you get to 1440p and 4k, there is very little difference in fps based on the CPU because the GPU has to work much harder at those resolutions.
I agree with KingV, if your monitor only has 60hz, then you should not get a 1080ti. However, if you monitor is a 144hz panel, then the 1080ti will be a great choice for first person shooters. You will have very high framerates making the game play butter smooth.