I7 7700k with the 1080 ti will obviously be ideal, but if you aren't planning on overclocking, save money on the non k version. Also keep in mind that if you get the K version you will need to purchase a CPU cooler as well.
The amount of difference overclocking can make is a matter of perspective, but in this case, a stock 7700 vs an overclocked 7700k could be upwards of 15-20 fps difference in some games. In my mind, that's a pretty substantial difference, but I'm sure not everyone will agree with me on that.