I youst found out that my Ram has only 1600mhz what i suspect is that only 80% of the memory is ussed but the comunication with the other components is to slow at 1600mhz
About the gpu. I dont think thars it because it stuters at min as well as max grafik setings.
From what its sound it would be best to get a new motherboard and a beter cpu that can use ddr4 and put on 16Gb of 3600Mhz ram