These graphs compare the initial values from the 2011-12-15 kernel (blue) to the current IPv4 (red) and IPv6 (green) values of 2012-04-08 showing improvements.
We can see that compared to the initial values, TCP IPv6 perforamnce has improved in both cases, withouth and with offload support, the latter making a significant difference.
Looking at the graphs comparing to IPv4, we can see that we are at about the same level with offload support, the median slightly lower than on IPv4 but seeing higher peak values on IPv6.
In case without offload support however the changes did not make a significant improvement. The one change equally applied to IPv4 seems to also have improved the situation there.