I don’t have access to the latest hardware. Internet-published PCIe gen4 x16 throughput data that I have seen measured by others was in the 23.5 GB/sec to 26 GB/sec range, so about 2x the PCIe gen3 x16 throughput of about 12 GB/sec commonly observed. Which is as expected based on the respective PCIe specifications (16 giga transfers per second vs 8 giga transfers per second).
Those sources that performed application benchmarks generally showed only small (< 10%) performance differences between running with PCIe gen 3 vs PCIe gen 4. That does not mean there could not be a use case that benefits heavily from the faster link, but it is also not surprising since various existing compute applications I have looked at use only 20% to 40% of the full PCIe gen 3 link bandwidth.