Disabled IPv6 on DockerNAT adapter.
Set IPv4 DNS to 8.8.8.8 / 8.8.4.4
Reboot PC. Stalled. Forced shutdown. Restarted.
$ docker run hello-world successfully pulled the latest!
Docker 1.11.1-beta13 build 3441
Windows 10 Pro Insider Build 14342
(The Docker update wasn’t what fixed it, even after reinstalling the beta.)