In the USA, around 50% of Google traffic and 60% of Facebook traffic goes over IPv6. The largest mobile carriers in the US are nearly entirely IPv6-only too (customers don't get an IPv4 address, just an IPv6 one), using 464XLAT to connect to legacy IPv4-only servers. I'm sure we'd know if routing with IPv6 was slower. Google's data actually shows 10ms lower latency over IPv6: https://www.google.com/intl/en/ipv6/statistics.html#tab=per-country-ipv6-adoption