Unless you can sell your 970s to compensate the cost of a 980TI, I would just stick with what you have. The performance between the two is nothing, but what it would do is give you the ability to do SLI 980Tis down the road, less power consumption, less heat generated by SLi and less headaches of poorly optimized games for SLI and extra vram that you dont have right now. It would be more of a lateral move though, so I wouldnt expect any performance increases. 2x970s=980TI in most cases.