HIBI
... I disabled "Intel EIST" and "C1E Support" on BIOS (mine was AMI BIOS) then stuttering was gone. (Maybe these are called C-STATE Tech, Enhanced HALT State and etc on the other BIOS)
Excellent suggestion. OP said he tried "all the optimizing suggestions" but some folks tend to forget about (or are afraid to mess with) anything in the BIOS. This one is definitely worth trying if he hasn't already.