is your apparent speed loading pages better with IPv6 off? There is only one IPv6 DNS for the entire US whereas there's 4 or 5 more local ones with less hops for IPv4 making rout resolution somewhat faster.
Seems that mixed IPv4 and IPv6 causes a slowdown for some users.
unknown if they ever got phone and IPv6 working in the same gateways, I know biz class installed seperate modems for phone and data to get IPv6 reliable
I can't say if the speed is different with IPv6 ON, but things haven't gotten any slower with it being turned OFF.
Turning IPv6 ON in my router causes some errors to get logged in the router's logs, like the linux kernel "net-ratelimit: callbacks suppressed" log messages.
I think something in the IPv6 implementation is flooding the linux kernel in my rouer with all kinds of log messages, and the kernel thinks it's a DoS attack on the syslog.