Could vary depending on where your connection terminates, but last time I set this up the speed was abysmal.

I've got a 8Gbit symmetric fiber connection (with no IPv6 at all, yay) and regularly make use of all of it, so I'm well connected. Router hardware is more than capable of the encapsulation.

With the HE tunnel up, I was often getting tens of megabits per second for any endpoints that supported IPv6.

Works as a "this endpoint is _only_ available on IPv6" so I can connect to something I couldn't otherwise, but day-to-day the experience is vastly better over IPv4 for me.