I'm trying to bring forward IPv6 support of squid.
FYI: You can try to use Web Polygraph to test performance aspects of IPv6 support in Squid. For example, it may be useful to compare IPv4 and IPv6 performance (with or without DNS) on an otherwise identical workload. You can start with a standard workload and then modify it to intensify operations that affect IP version the most. I do not know if anybody is actively using IPv6 code in Polygraph now, but it used to work.
HTH,
Alex.
