At the moment I have a KFA2 EX OC, Z170-eMobo, I76700k, 16GB RAM 2400hz. I have just got a 4K TV and just wounded how much of a boost I would get from a 1080 to a 1080TI. I have had this PC since September 2016 but want ultra 4k settings and 60FPS. You think upgrading to a TI be worth it or buy a new PC with a 2020 and up to date PC?>
GPUs are due for a die-shrink in 2019 down to 7nm from the 16nm for both the Nvidia 10 series and AMD Polaris and Vega (Nvidia 20 series are on 12nm), so going from 16nm to 7nm should seen a pretty decent jump in both performance and power efficiency.
My suggestion would be don't get too hanged up with maxing graphic settings...your 1080 should be good enough to manage games at 4K at med settings at 40~45fps+. The chances are once you start gaming, you wouldn't really care too much about the graphic difference between max and med (though 40fps may still be the key issue as you would really notice it without and sync tech).
You could also consider dropping the res down to 3200x1600 as a middle ground as a reduction the load on the 1080. And if you not already done so, overclocking the 1080 would definitely help.
I don't really think you would need to upgrade your PC since you are only aimming for 60fps at 4K, not like 100~144fps at lower res which where CPU bottleneck would more likely to occur, but again you would definitely want to overclock your CPU.
Also the stock of 1080ti has pretty much almost depleted from retailers, so the price have shot back up comparing to a month ago.