How robust is the V6 to V4 infrastructure?

A question came to mind with all the discussion of ipv6 vulnerabilities. I am wondering for those with a lot of real world pure IPv6 connectivity, how robust have been the V6 to V4 gateways necessary for intercommunication between native IPv6 hosts and the IPv4 world? I was thinking that going to native ipv6 depends heavily on these gateways being reachable and having fairly high performance characteristics. How are the service providers doing providing these services?

Steven Naslund
Chicago IL