I've got a photo in my archives somewhere of 405KTs on the DME in a 421 C @ FL250, some moons ago.
Got me into one of them jetstream thingies outa Perth en route to MEL, as it turned out I coulda made MEL direct, when I got back up into it, but chickened out at ADL.
"Say again your flight plan amendment times"
Had been following a GV around Oz for a week or so, he had been on a sales demo and I had been paddling around checking the traps.
He departed in front of me on climb to FL350 but requested reclear back down to FL250, as he found the jet with his flash gear on the way up.
It was only forecast to be 100 odd KTS but turned it on for us at over 200KTS.
Sparkling clear winter Sunday morning, smooth as silk.