What is the true top speed of the SR-71? By "true" top speed I mean the absolute fastest horizontal airspeed the aircraft can achieve if damage to the engines is disregarded (similar to how the MiG-25 apparently can reach mach 3.2 but may damage its engines beyond repair). Catastrophic structural failure (of anything beyond the engines) is not permissible in this scenario.

In "The Untouchables" Brian Shul claims that he reached mach 3.5 while evading a missile. This is also stated in the Wikipedia article on the SR-71 with a citation to the same book.

Are there any other sources than his own book that can confirm or reject this claim? Can it be argued for or against this top speed claim on technical merit or physical limitations?

On Wikipedia it is also stated "Maximum flight speed was limited by the temperature of the air entering the engine compressor, which was not certified for temperatures above 800 °F (430 °C).[57]"

However, it is not clear how much abuse beyond this the compressor could take. It is possible to give some estimate or educated guess based on the materials used?
Based on the SR-71A operational envelope, the top Mach number was Mach 3.3 when authorized by the commander and Mach 3.2 otherwise. The top airspeed was 400 kts equivalent airspeed when supersonic and 450 kts equivalent airspeed when subsonic.