your CPU is still pretty capable on handling the 1080ti, although on CPU demanding games the CPU might bottleneck it a bit (not too much, but should be viewable)
it is however, a worthy upgrade imo 😀
if u're still planning on using the GPU for 1080p gaming, the old 970 is still sufficient
however, for 1440p 144hz / 4k though, the 1080ti is the way to go 😀
Edit: by viewable i meant that fps difference between kabylake and haswell is noticeable at some point, but nothing too worrying imo XD