This question will be resolved as soon as a review is published by TechPowerUp. The performance comparison will be based on the average frame rate achieved by the standard variant of the GPU at 4K resolution. Currently, the RTX 4090 achieves an average of 109.2 FPS, as reported by https://www.techpowerup.com/review/intel-arc-b580/31.html :

If the RTX 4090 maintains its frame rate, the new flagship GPU would need to reach an average of at least 218.4 FPS to be considered "100%+ faster".

If TechPowerUp doesn't publish a review, I'll use some other source, like e.g. TomsHardware.