4090 is a 450W part while the M2 ultra GPU portion is approx 70-80W.
For 3D raster performance it cannot match the 4090, but is more than 50% of the speed for 1/6 the power.
The 4070Ti is a 280W part and has the same performance as the m2 Ultra on this benchmark.
Another data point is gfxbench:
The first unified cross-platform 3D graphics benchmark database for comparing Android, iOS, Windows 8, Windows Phone 8 and Windows RT capable devices based on graphics processing power.
gfxbench.com
The M2 Ultra matches the RTX4080 and is approx 65% of the 4090.