They have done a lot of optimisation on PUBG in the past 2 years. I used to have 30FPS in many areas with a GTX1080 in the beginning. Stutter still occurs in some areas where the assets have issue. Specifically I noticed that some stairs leading up into some buildings cause frames to momentarily drop to below 40 FPS while average framerate is over 100.
I did help someone upgrade from a 1060 to 1080 and it did still significantly improved smoothness. Those pesky low FPS moments are now much less. I would say yes upgrading will help, and you need to make it worthwhile. E.g. at least GTX 1080, 1070ti or RTX2060. Then you can also think about getting a better CPU but that would be second price. The 6600k is still OK and a 7700k like mine (which is still one of the fastest CPUs for PUBG) is 15% faster in single core than your CPU which I dont think is worth upgrading yet. I find that overlcocking my GTX 1080 founders edition to 2000Mhz immediately makes noticeable difference for me.
So in short, Upgrading your graphics will make a difference and also getting a 144Hz monitor makes a huge difference especially during aiming in high tense fast paced turning scenarios.