First times I asked this, I had suspicious PSU, but now I have new PSU, thus I can ask it again.
ASRock Z97 Extreme4
32GB DDR3 2400
3 WD Black 1TB
PSU Corsair RM1000x
open air test bench, here is winter (room temperature is usually around 15C or less)
Windows 7 64Bit
drivers tested: 16.3.something, 16.4.something, 16.6.1, 16.6.2
GPU: Sapphire Nitro 380X 4GB
The problem: The GPU stutters quite a bit, in some games it is more obvious than in others, although I don't own Just Cause 3, this video shows the issue I am seeing perfectly: Just Cause 3 PC: GTX 960 vs R9 380, Core i5 4690K vs FX-8350 Performance Testing - YouTube
Other tests: GTAV in some versions (16.4.something) is almost unplayable, sometimes having fits of heavy stuttering, on 16.6.1 it "mostly" works, sometimes it still stutter, but it is rarer.
Many demoscene demos, and older games behave weirdly (for example getting capped at some low FPS, usually around 40fps, no matter the game or demo)
CAD programs the mouse stutter, zooming, rotating, etc... also cause stuttering.
Unigine Heaven has obvious stuttering nearer the end, with average framerate high, maximum framerate also high, but visible pauses on the video mid-scene (ie: not on scene transitions), usually when nothing special is happening (ie: no new effect or geometry). mininum FPS on unigine heaven is 5 fps.
OCCT, the GPU stays for about 50 seconds stable, then the FPS start to slowly drop. I couldn't figure a way to track frametimes, and the scene is mostly (or completely, depending on the settings) static, so I can't see stuttering.
stuff I tried so far:
disabling ULPS, raising power limit to +20% (it helped a lot in some games), changing drivers (some games get better, others get worse, most noticeable so far on GTAV, that the performance varies wildly depending on driver version), DDU, replugging GPU, replugging power cables, overclocking CPU, underclocking CPU, over/underclocking RAM, undervolting GPU (performance improves, stuttering diminishes, but it crashes more often... on default settings it also crashes, but less than undervolted), overvolting GPU (performance drops A LOT, stuttering skyrockets), enabling/disabling vsync (usually make no difference), enabling "performance" in the driver (right clicking the driver icon).