We measure system-wide power draw from the wall while running the 3DMark Time Spy stress test for 30 minutes.
We also use Nvidia PCAT to measure power draw of the graphics card only, with readings from both the PCIe slot and the PCIe power cables combined into a single figure. This provides us with significantly more accurate data to work with as it is measuring only the GPU power, and not total system power which is a fundamentally imprecise measurement.
Graphics card-only power draw for the RX 6700 XT averaged 222W over our testing, which is just an 8W reduction versus the RX 6800. That puts it 5W higher than the RTX 3070, though that doesn't bode well for overall efficiency considering the RTX 3070 is the faster card.