Even better:
A G5 en route from Moscow to the Caribbean which entered London Airspace at FL550. When asked, he said his planned time en route was 13 hours, and when he got there he would still have an hour's flying fuel left with reserves!
Edited to say: The semi-circular rules do not ALWAYS follow convention: South of ORTAC Brest Control use conventionally Eastbound levels (330, 350,370 etc) for Westbound (= Southbound) traffic due to conflicts with crossing traffic over the Brest peninsular.
In addition, the core Oceanic tracks use every level to maximise capacity. There is no opposite direction traffic on the core tracks so they can all go at 290,300,310,320,330 etc