IPv6 performance via TunnelBroker always very poor compared to native IPv4

[JenkinsNET]

I have been using TunnelBroker for a few years now and all the while I have observed that performance (as measured using various tools) over the IPv6 tunnel is very poor compared to my native IPv4 performance; the IPv6 tunnel only delivers around 10% of the throughout compared to IPv4. Since a lot of my stuff uses IPv6 now this is becoming a big issue for me. My ISP is Virgin Media and I have a 200 Mbit downstream / 10 Mbit upstream connection which I monitor rigorously and IPv4 performance is always very good (it does vary a bit based on time of day). IPv6 performance via TunnelBroker is however routinely very poor as noted above. My tunnel is configured on my Apple Airport Extreme (latest generation) router based on the TunnelBroker recommended setup and apart from the performance it works flawlessly. I am connecting to the remote server on 216.66.80.26.

Is this poor performance expected/normal? Is here anything I can do to improve it?

Thanks for any suggestions.

[broquea]

Contact your ISP about native IPv6. You are using a free and shared platform with hundreds if not thousands of other users on a tserv. Speed parity should not be expected. You can also try tuning TCP windowing, MTU, MSS, etc.

[JenkinsNET]

I'd love to get native IPv6 from my iSP. Sadly my ISP is Virgin Media who *still* haven't said when/if they plan to deploy native IPv6 service  :(