MTU of the Internet?

perhaps this is one of the not-so-obvious benefits of running a web
proxy cache such as squid. the greater internet can have larger
packets floating around, and the local proxy of the ISP can deal with
horrible tcp stacks, retransmissions and client machine with small
receive buffer sizes.

And imagine having 2 interfaces on this machine, one with MTU=1500 and
one with MTU=576.