There are a bunch of threads of people with similar complaints, the most common proposed solutions are increase power limit by 20% on the control panel, and disable power saving.
Doing that DOES help, and in many games the obvious stutter go away, but looking at the GPU clock graphs, the throttling is still there, just much less strong.
I am of the opinion that the card should work out of the box correctly, if you need to go past the overclock warning to set +20% power limit, something is already wrong.
And then, even with +20%, the thing still throttles, much less obvious, almost imperceptible, but it does.
My personal theory is that it shipped with a bios with too low TDP.
How I test if that is true?
Also, nVidia GPUs have a nice feature where they tell you why they are throttling, no such feature on AMD?