Terry Casey wrote:

Interesting - I've just run the test from via my VM connection
and got precisely the same answer as you?

Any more volunteers?

"From the tests we did, we can assume that 1472 bytes is the largest
unfragmented packet size. The MTU size would be 1500, made up from 1472
payload and 28 ICMP/IP Headers and payload information."

But then I know I have 1508 byte baby jumbo packets on my PPPoE
interface, hence full-fat 1500 byte "inner" packets.