I am currently measuring RTT from ASN4717 to several dual stack IPv4/IPv6 servers in Indonesia for every 5 minutes.
It is clear that IPv6 RTTs are not symmetric with IPv4 RTTs because of different path/routing between IPv4 and IPv6. NTT and CBN are exception. Their paths are symmetric from AS4717.
Above graphs are also available on http://sfc-monitor.ai3.net/~dikshie/indonesia/ (IPv6 only)
If you need the data (only available in RRD format) please contact me.