I had what I believe to be the same "periodic microstutter" bug that you are describing. The game pretty concistently stuttered/lagged once every 10 or so secconds. What fixed it for me was updating to the latest Nvidia Drivers. No amount of tampering with graphics settings, setting them to the highest possible or the lowest possible values did anything to the stuttering so I figured it had to be a driver mismatch of some kinda AND my Drivers were well over 6 months old. If that doesnt work I did remember POE1 having some weird stutter on some computers that went away by disabling extra wireless/bluetooth networks that you may have, I happened to have one and I disabled it too while the drivers were installing but I doubt that was the fix. Mentioning it anyway just in case.