Definately fastest at low level - chased down F-111s and B-1Bs trying to do their best as well! Don't forget that her design spec was to shoot down BEARs and BLACKJACKs low level over the North Sea, so speed was a large part of the key user requirements (or whatever they were in the 70s).
The picture in Wales above ^^^^ shows her clean winged as well. I remember when they arrived from Warton like that and M2.1 to 2.2 was quite easy at ~40-45kft.
LJ