I have a Sapphire RX 470 Nitro+ OC (got it today) - 1260Mhz, 4GB 7Ghz RAM
In its stock configuration the thing is a real power hog - using almost as much as my R9 290 at 940Mhz (reference clock) without always performing any better.
TessMark - (set 4, insane, 1080p fullscreen, 8x AA, no post FX)
GPU - SCORE - POWER
R9 290: - 5372 - 312W
RX 470: - 6516 - 300W
Heaven - x64 Tess (1080p, all maxed)
R9 290: - 1390 - 300W
RX 470: - 1521 - 294W
Heaven - No Tess (1080p, all else maxed)
R9 290: - 2260 - 312W
RX 470: - 2203 - 300W
Valley - Extreme HD
R9 290: - 2336 - 330W
RX 470: - 1976 - 300W
GPU - AVG - POWER
Hitman - DX12, 1080p fullscreen, FXAA, 4x anis, all else maxed.
R9 290: - 66.5 - 368W
RX 470: - 58.0 - 354W
Battlefield 4 - DX11 1080 - Ultra
R9 290: - 100.0 - 380W
RX 470: - 102.4 - 372W
I thought these results were terrible, as you might imagine. So I did some checking on the RX 470 for its power draw behavior at different frequencies:
This is the system power usage delta over idle (120W). Notice anything funny?
For reference, here's the R9 290 in the exact same system, exact same setup:
Clearly something artificial was going on (and the card throttled at 1275Mhz, despite a +50% power limit and 100% fan speed (~65C temps)).
Long story short, the default BIOS (the OC BIOS) sets a GPU voltage of 1168mv. Can you guess when that kicks in? Yup.
So, I undervolted the card. A lot. By 150mv. The card is perfectly stable (been testing it all day) at 1025mv at 1250Mhz. And the power draw is an entirely different story.
R9 290 vs RX 470 (both properly configured for optimal efficiency at each frequency):
We can only go as far as the R9 290 will go before throttling, so it stops at 1150Mhz. The RX 470 only pulls 210W at 1250Mhz under Furmark when not being allowed to throttle.
On a side note, the RX 470 is definitely not memory bandwidth starved. I can't find a single benchmark that shows gains with increasing memory clocks - and I clocked in 50Mhz steps all of the way to 2100Mhz. Power usage went up slightly, and minimums went up slightly (~1FPS), but that was about it.
Also, Power Efficiency mode is quite nice, IMHO, when you have the card configured to also not throttle (so you don't get stuck in lower frequencies while gaming).
At 1150Mhz, in TessMark, RX 470 is 2.45x more efficient than R9 290. In Heaven, with x64 tessellation, it is 2.5x more efficient. With my under-volting on both cards - both in their best light.