Simple answer, to run samp at 120 fps, u need a good GPU (recommend GTX 1050 atleast). I have the same specs u just mentioned, i5 7th Gen with 8GB ram but I get 80-90 fps on recording ( don't compare with my last video, my video editor fucked it up)
Edit: Forgot to mention my gpu, my laptop does not have a gpu, just Intel HD 620 integrated graphics