After applying the latest update from Apple, I re-ran the Geekbench build test on the i9. It’s slightly faster, but processor frequency stays stable when building (which is comforting).
Still technically slower than the i7, but close enough that, practically, it doesn’t matter.
It’s thermally constrained. The processor is at 95-99C consistently throughout the test. Both the i7 and i9 run all cores at ~3GHz.