Any difference with hw acc disabled in browser ?.
You must've misread. Browser is irrelevant.
Power Efficiency is performing as expected according to your post. With it enabled GPU clocks are throttled to use less power, with the option disabled clocks are higher to improve performance, at the expense of using more power. No harm is being done to your GPU by having a high clock speed while playing videos. If you are still concerned, try disabling hardware acceleration in MPC and that should give you lower clocks.
Sorry for raising this, but the thing is most certainty NOT performing as expected.
It has been over a year now, and still this issue is still not fixed. Hardware accelerated browsers or video players should not raise clock speeds of these cards. These cards are perfectly able to do hw accelerated browsing or videos, or running desktop on their idle clock.
I don't understand why this issue is still a problem when the solution is so simple:
Option 1 : Give us per profile power efficiency toggle, so we can do your job for you, and optimise our cards.
Option 2: Separate 2D / 3D power efficiency profile, where it enables itself when no 3D app is running ( conserving power, reducing heat ), and then it auto turns off when ingame ( giving performance we want out of these cards )
Even more bizarre, idle / load clocks work perfectly fine in older gen cards..
My workaround was having PE toggle ON, for efficient idle / office use, and having 3rd party app " clockblocker " per app ( game ) preventing downclocking.
Recent drivers tough, have messed up PE toggle, so it now toggles to off randomly and very often, making my workaround useless.