Thump,
I would think if they (B-52s) were airborne at the 7k they were not heavily loaded. Those runways were built for worst case max effort hot day take offs. That is probably what drove the original length.
While F-16s can take off in 5-6k it eats up even more on landing. I think their min runway length is in the 7-8k range when operating clean. The F15 min length was 1K less in the clean configuration and could be waived lower by the OG/CC. We both required cables at least one end of the field.
Cheers,
Biff