Power, Temperature and Noise
The difference between the two Asus boards is about 25W at the wall. Perusing both boards' logs shows the RTX 3080 card alone pulls 337W and the RTX 3090 354W.
We marvelled at how low the RTX 3080 TUF Gaming OC was able to keep the GPU under full chat. The RTX 3090 is similarly impressive.
The two ASUS cards use ostensibly the same cooler but the fans on the RTX 3090 need to work harder to keep the temperature in check. Part of the extra noise may also be attributed to greater levels of coil whine present on this model, especially when games run in excess of 100fps, which is often.
Loading menus in particular, where framerate is high, cause this sample to exhibit higher levels of coil whine than on any RTX 3080 we have tested, including the Asus version.
Switching to the quiet BIOS reduces noise to 37.4dB though temps go up to 73°C. There's no clear reduction in performance, either, so we'd prefer that setup for quieter computing.