Not really accurate. The switch from NRZ to PAM4 actually massively increased the bit error rate. They switched away from the 8b/10b style line code and replace

Not really accurate. The switch from NRZ to PAM4 actually massively increased the bit error rate. They switched away from the 8b/10b style line code and replaced it with forwards error correction. PCIe 6.0 uses 256 Byte frames, with 242 Bytes of data, 8 Bytes or CRC and 3 Bytes of error correction. So it actually has way more overhead than the older versions and their 128b/130b line coding, It's just at a slightly different layer.