DNS Shotgun is capable of simulating real client behaviour by replaying captured traffic over selected protocol(s). The timing of original queries as well as their content is kept intact.
This came across the NANOG mail list.
A Longitudinal View of Netflix: Content Delivery over IPv6 and Content Cache Deployments
Caches reachable within 6 IP hops and 20 ms
-IP path lengths shorter by 40–50%
-Latency lower by 64%
-Throughput higher by factor of three
-Latency benefits more pronounced over IPv4 compared with IPv6
Latency and IP path lengths similar between both address families
⇒ High IPv6 preference, however, slight drops during peak hours