Did 5.40 in a K8 on my silver duration. It was a red hot summer's day so I took off wearing shorts and a polo shirt. Spent most of the flight at around 7-8k and came down like a block of ice. Lesson learned.
Longest trip P1 in powered so far is 2 hrs and that was long enough, I just can't imagine what 20 hrs in a light a/c must be like. I do the Brisbane run every year and 13.5 to Singapore in the comfort of a passenger jet is brain aching enough.
Incidentally, I'm just doing my IMC rating and did a PAR approach today in real IMC, was totally blown away to see the runway lights appear at 600 ft on the nose. Good innit.