Out of Narita to Nadi in Fiji, just at top of climb we hit 698kts G/S.
It made up for the 330kts G/S on the way in!
Anyway, here's the fastest I've gone in level flight in anything -
http://www.billzilla.org/reallyhighmach.jpg
Mach 0.915, hand flown whilst taking the picture. The plane started to nod up & down slowly past about 0.9 odd ....