Right, but my point is, most US ISP are shitty and don’t offer IPv6 blocks. If you are in the lucky minority who’s ISP does provide proper support for IPv6, then why bother dealing with IPv4 at all, ignore it. Almost nothing needs it anymore besides the majority of ISPs in the US which all suck.

There are some cases where locally defined addresses (private IPv4 or IPv6 ULAs) and NAT are useful for controlling what people and devices on your LAN can access, but usually not in a residential or home lab situation. So why bother. Either if your ISP offers proper IPv6, just use that, or if they don’t, just use IPv4 and ignore the transitional IPv6 addresses. With both you end up writing every NAT and firewall rule twice, I don’t see the point unless you have an old device that can’t handle IPv6.

As for performance hits, I was referring to the fact that most ISPs dont offer proper blocks of IPv6 and the transitional technologies they do offer like 6rd or 6to4 do have performance hits, sometimes extremely significant ones. So if you implement dual stack and your DNS query returns AAAA record and your systems prefer it, they will always take a hit. This is from lots of experience. I always disable IPv6 because my ISP uses 6rd and it is the only one in the major city I live in that offers >10Mbps upstream, so it’s not feasible to switch. When I was on Comcast and got an IPv6 block, I disabled IPv4. Dual stack would be too much work.