Constant random stutter/hardware lag when playing.

So when OW launched my PC was relatively fine and I could get smooth +140 fps for everything. Recently however my PC has been a complete toaster handling this game having constant long stutters/pauses during gameplay and its really been a pain in the ass to try and fix it. I've tried different res' and gfx settings but nothing seems to work. Anyone care to point out which of my pc components is the elephant in the room and what i need to upgrade/fix. I'd like to play this game without this shitty lag for once.

CPU - Intel i5-4690K @ 3.5GHz
GPU - AMD Radeon R9 380
RAM - Corsair Vengeance 8GB

recent windows 10 update has made my pc freeze upon start up. it makes it through every time, though it'll freeze and take 15-20 seconds more.

DId you give it a good cleaning ? Opening it and removing dust, running Ccleaner and stuff ?

I experienced the same issue recently dropping from 160ish stable fps to 80ish. It was actually due to all my graphics settings being reset to maximum by a driver update from geforce experience. You're not concerned by this but you could still check your in-game video settings (edit : didn't read your message properly)

Oh man this can be so many things. The first one to check is cpu throttling. Get intel extreme tuning utility. Dont change any of the overclocking settings. You are going to use the graph at the bottom. Add these to the graph if they aren't already there: every limit or throttling indicator, cpu core speed, and cpu max core temp. Play the game untill you see the stutters then check the graph. If your cpu core speed dropped, if you saw some limit/throttling indicators on the graph, or if your cpu temp was too high (over 90 you will throttle for sure, over 80 is pretty damn hot, over 70 can throttle on laptops) then you are throttling. If you see your core speed drop then you can try to improve the cooling or undervolt your cpu and that should help. You might have to repaste your cpu which should be pretty easy. I recommend using some thermal grizzly kryonaut.

ddu, reformat, whats psu? If you can, try testing with different ram/mobo assuming ur cpu and gpu are fine