My he.net ipv6 tunnel adds about 2ms of latency on average, which I can totally live with.
As an aside, they also want to ping your IPv6 daily (at least in my logs) to keep the tunnel alive; otherwise quite stable.
I'm fortunate to not have to deal with CGNAT. But still waiting for IPv6. A he.net tunnel works for now for what I need: stable IPv6 for SSH tunneling from my IPv6 mobile.