I'm told by some folks who run core networks for a living that while the routers may sling IPv6 packets as fast or faster than IPv4, doing so with ACLs, filter lists, statistics, monitoring, etc., is lacking. What's worse, the vendors aren't spinning the ASICs (which I'm told have a 2 to 3 year lead time from design to being shipped) necessary to do everything core routers are expected to do for IPv6 yet.
This may mean that you are better off building an IPv6 overlay using tunnels over an IPv4 core, or using MPLS with 6PE. These are the sort of detailed questions that people should be asking their vendors now. Will you really be able to get the expected work lifetime out of the boxes that you are buying today?
I thought parts of the USG were under a mandate to be "IPv6 capable" (whatever that means) by this summer. If there is a mandate to be running IPv6 within the USG by the end of the year, people are going to have to get very, very busy very, very quickly.
Lots of the USG and DOD folks are buying Hexago boxes which basically means that they are going to talk IPv6 to each other using tunnels over an IPv4 core network. --Michael Dillon