The standard runway length was set at 9000 feet. In the late 50s- early 60s the Mark 1 aircraft would use much of that length. A fully laden Victor 1 in high temps with 21x1000lb of bombs used over 8000 feet.
A Valiant, carrying a 10000lb store would not have been far from that.
The Mark 2 Vulcan on the other hand, fully laden, could probably get off in well under 6000 feet IIRC.