The most slippery ones were the ones from the factory at Warton. No pylons and fuel control units not wound back!
I did hear anecdotally that a crew did over 1000kts and that the pilot thought he was doing 999kts - unfortunately the numbers stopped at 999 in the HUD and the Nav's Tac displays showed somewhat more in TAS at low level over the sea!
Here is a 'slippery one'...
No Norris McWhirter around at the time, though...
LJ