Cards like the Sapphire NITRO+ RX Vega 64 and other AIB cards suffer from high idle temps of 50c because the HBM clock is always at 945mhz when using 3x 1440p 144hz monitors. If I run them at 120hz or lower, the memory clock will idle at the correct value of 167mhz. This wouldn't be a problem if the AIB cards didn't shut the fans off at temps lower than 60c.
When running the monitors at 167hz for 60hz, 100hz, or 120hz refresh rate, the Vega 64 HBM memory clock idles to 167mhz resulting in an idle temp of 38c.
When running the monitors at the max advertised 144hz refresh rate, the Vega 64 HBM clock idles at 945mhz (the max clock state) resulting in an idle temp of 51c. The idle power consumption is also increased to 15w.
The same behavior is observed on the Vega 64 reference card, however, the workaround is to set the fan profile in Wattman to run minimum at 900rpm which makes the fan behave the same as the idle fan speed on the GTX 1080 Founders Edition.
Comparing to the GTX 1080, which is using the same monitors. Even at 144hz on all 3 monitors the idle memory clock is 139 MHz with an idle temp of 33c. These small details are the things that AMD needs to improve the Radeon brand image. I wanted to make a video demonstrating this behavior as techpowerup's reviews already show this functionality is something that is being taken into account when making purchasing decisions.
I understand this is probably done for some reason pertaining to response time but, the competitor has managed to run multimonitors at high refresh rates and still keep the memory clock low even when watching 60fps youtube videos. There is no reason why Radeon can't do this as well.
If that's the case it's the same bug that Nvidia had solved long ago where the memory clock was at the max clock when using 144hz.
Here is a screen shot of what it looks like on the reference card when I have all 3 DisplayPort monitors on 144hz and the fan profile is set to 900 rpm minimum over the default in order to maintain the normal idle temperatures. This is a valid workaround for the Reference card only because the custom cooled cards such as the Sapphire Nitro+ cannot have the default fan profile modified in anyway either through Wattman or 3rd party apps like Afterburner.
AMD Vega 64 Reference Card (All 3 displays at 144Hz)
We can see from this the incorrect behavior resulting in a higher idle power draw and higher voltage of 0.95v.
This custom fan profile is only valid for the Reference Cards. Changing it on the Sapphire Nitro does not disable the zero rpm feature.
For now, when using the custom AIB cards such as the Nitro+ I have to run the 2nd and 3rd monitor at 120Hz in order to drop the GPU idle memory clock to 167mhz.
Here is what it looks like on the Sapphire Nitro+ with the primary display (center monitor) on 144hz and the side monitors on 120hz.
Sapphire NITRO+ RX Vega 64 (Display 1 144Hz, Display 2 120Hz, Display 3 120Hz)
As you can see from this behavior, different display running at different refresh rates do not prevent the GPU memory clock from idling at the low power state which is good news because this is something that has plagued GPU vendors for many years. Here we can see the expected power draw of 3 watts and a voltage of 0.7688v.