[X-Istence]

The performance penalty is that now my packets travel:

Phone -> T-Mobile -> NAT -> T-Mobile -> Internet -> My hosting provider

Whereas with IPv6:

Phone -> T-Mobile -> Internet -> My hosting provider

That NAT is an extra step, and will add a small amount of latency.

[Dylan16807]

The NAT, if set up right, would not cause the packets to take a different route.

Changing the packet format requires nanoseconds, no more than normal packet processing.

It's possible to set up anything wrong, but there's nothing about this technology that would introduce latency when done correctly.

[djrogers]

That NAT in many cases happens on the same edge router that'd be dropping your packets off on the internet anyway, so it doesn't have to add an extra hop.