SR71.
FL80 Mach 3.0
Now Mach 3 at 8000 feet really would be something. Presume you meant FL800.
Had a similar conversation with an F/O a few years ago, of our perfect pair of aircraft. As far as I can recall mine were Spitfire/Lightning(EE version) and his were extra 300/F15. There were many other close contenders, including, but not limited to, Mustang, Hunter, Lancaster, Jungmann, Me262 etc