Without wishing to be a pedant, the relationship also depends on gamma, the specific heat capacity ratio.
BelArgUSA,
If you check
http://www.sr-71.org/blackbird/manual/5/5-8.php you can see the max Mach limitation for the SR-71 was also really a CIT of 427C. See also
http://www.sr-71.org/blackbird/manual/5/5-10.php
I once worked out that in ISA-50C conditions (or thereabouts), this theoretically allowed for a Mach number of 4.
A significant number of SR-71 crews exceeded 3.5 I believe. Certainly, in the book
The Untouchables you can read about a crew who did.