I think the rationale is that some ISPs offer their customers IPv6 as well as IPv4, with IPv4 behind a proxy/NAT and IPv6 routed directly. In this case, the lat

I think the rationale is that some ISPs offer their customers IPv6 as well as IPv4, with IPv4 behind a proxy/NAT and IPv6 routed directly. In this case, the latency for IPv6 will be lower/better.