> Google has measured to most customers about 20ms less latency on IPv6 than on IPv4, according to their IPv6 report.

I've run that comparison across four ISPs and never seen any significant difference in latency... not once in the decades I've had "dual stack" service.

I imagine that Google is getting confounded by folks with godawful middle/"security"ware that is too stupid to know how to handle IPv6 traffic and just passes it through.