ha lark it can be double the speed. this does not always translates in some games an fps boost.others ,youmay be able to have ultra graphics settings. there are reasons why people decide on a better gpu other than fps increasing.
. real world example. I have 2 rigs. both cpus i7 stock no overclocks.
one with an i7 gtx 970 , the other i7 gtx1070.
I play arma3 a bit. on similar settings both will get around 50 fps . because Arma3 is a cpu game, ai ,big maps ,lots of calculations, old engine.
here's the differences. number 1 -on the gtx 1070 I can run a 1440p monitor(imo looks way better ).2- I can crank up view distance thousands more same with the objects view distance. this is what the gpu does in these games cases. makes the game look better overall.
the reason i'm explaining this is so you understand the reasons people need that twice the speed and it does not translate always into fps because of the games. in your case going from a gtx1070 to 1080 . is not advisable too little a jump. and unless you running 4k or vr it does not make sense. down the line maybe a gtx1080ti would be a reasonable upgrade and by then a nicer price.
kingdom come is being made for consoles. let that sink in. your specs are going to be fine when the Iron out the release build.
if you want an uppgrade get a nice screen if you already on 1440p keep it is the sweet spot right now in gaming.