According to Apple, IPv6 is 1.4 times faster than IPv4 (latency wise AFAICT):
* https://www.zdnet.com/article/apple-tells-app-devs-to-use-ip...
This is supposedly "due to reduced NAT usage and improved routing."
It is great marketing to list 40%. But we need to know 40% of what. If it was 1ms, than 0.4ms faster isn't much of a performance.