Milt,
The subsonic cruise on Concorde was M0.95 (or M0.93 without the autopilot). The reason for this was that at higher subsonic mach numbers the shockwaves started to dance with enough asymmetry that the fly-by-wire elevons would work so hard that fatigue was a worry. M0.96 to M1.7 was driven through as quickly as possible.
Out of interest - the last thing you wanted when fuel was short was to go subsonic; this immediately lost 25%ish of your range - she was designed to efficiently super-cruise without reheat and that she did - Mach 2 was where she belonged.