See
Old Smokey's post in a previous thread on temperature/Mach relationships (and the rest of the thread, too).
As he states, temperature doesn't affect Mach or EAS. Since Mach and EAS are basically all you need to calculate drag, it follows that a fixed thrust will give a fixed drag, and since the drag-to-(Mach&EAS) relationship is unique (for a given Mach-to-EAS relationship, which is satisfied by the fixed altitude constraint), it follows you'll get a single value of Mach/EAS at a given altitude.