[Ozark Tom]

The Pratt & Whitney J58 documentation for that application covered a range of figures up to Mach 4.2, coordinating altitude, range, fuel burn rate, power derating based on altitude above FL72, etc. The chart curves indicated Mach ~3.2 gave the best range.

[Ozark Tom]

https://www.nasa.gov/centers/dryden/pdf/88507main_H-2179.pdf

http://www.ga153.com/aero%20space/Aero%20space%20information%20page/aircraft/SR.pdf

[lgjhn23]

"...The Pratt & Whitney J58 documentation for that application covered a range of figures up to Mach 4.2, coordinating altitude, range, fuel burn rate, power derating based on altitude above FL72, etc. The chart curves indicated Mach ~3.2 gave the best range....." Ah Yes! Here's my little souvenir from the early '60s that the engine development team had at the time. Even the coffee cups were classified back then.