[userbinator]

It's not clear whether they reached a limit of drive strength or latency (I doubt EMI is the factor, since he said those are shielded) but that's a good demonstration of the resiliency of self-clocked differential serial (and aggregated serial) buses. The technology is much closer to networking standards like Ethernet than traditional parallel PCI, with features like built-in checksums, error correction (newer versions), and automatic retransmit.