the 980 ti has more cuda cores, but the gtx 1000 series are clocked much higher, so its not as simple as cuda vs cuda count between maxwell and pascal. the gtx 1060 will replace the 970/980, the 1070 replaces the 980ti, and the 1080 and 1080ti/titan are in new territory. so the gtx 1070 and up will be faster than your gtx 970, but they will only help premiere run faster if the gtx 970 is a bottleneck. you can use GPU-Z to see the gpu usage (load) of your gtx 970 and see how much premiere is using it. if your cpu usage is near 80% or higher, and the gpu around 60% or lower, the cpu(s) may be the bottleneck.
some mixed info here on the gtx 1070 and 1080. i think its one of those reports you have to read between the lines, as not all the raw data was given and only a few tests were done.
gtx 900 series vs similar 1000 series, i would recommend the gtx 1000 series for future proofing and lower power draw, which should also equal less noise.
I just tested a 1080p project with a bunch of layers and the CPU was maxed out. the GPU peaked at 60%, but was mostly less. *Bugger*. CPU is overclocked 5820. Maybe I should overclock some more.