yes a old i5 which dont cut it for pubg.and a nearly 4 year old gpu.
modern intel and modern nvida card i should have said.pubg is a 2017 game.you need pretty modern stuff for it and even the highest gpu and cpu can drop in places at 1080.
if you want the best performance for 1080 res high fps. you want a 1070 gtx or 1080 gtx.they actually beat a 1080ti at 1080 res.price is pretty poor value on 1070 gtx at moment though.1080 probably better value but at 1080 res in pubg the fps difference is almost identical.
cpu wise if new wait for coffee lake.if you building your rig soley for pubg.intel is quite a bit infront as many benchmarks show for pubg.
what you could do is if doing a full upgrade is buy a gpu first see how it runs on your rig.if you find it exceptable (everyones different) then just play with new gpu or if still not happy upgrade mobo and cpu with coffeelake.
gpu benchmark