the question of the Blackbird's top speed is answered here:

Maximum Mach

Mach 3.2 is the design Mach number. Mach 3.17 is the maximum scheduled speed recommended for normal operations. However, when authorized by the Commander, speeds up to Mach 3.3 may be flown if the limit CIT of 427 degrees C is not exceeded.

A coworker of mine was an RSO on the Blackbird for several years (1985-90). He said normal mission speed was 3.15 but they could open it up to 3.2 if necessary. It seems the plane liked 3.2 better because the fuel consumption per mile was actually lower than at slower speeds. However, there seldom was a need to go any faster and if they were already at the design speed, they wouldn't have any more speed available if it became necessary for evasive action. He said that on really cold days they could go faster than 3.2 but it was seldom done. CIT (compressor inlet temperature) was the limiting factor.

The complete declassified pilot's manual is available online here. It makes for some interesting reading.

That RSO friend of mine has a beautiful picture of an SR-71 in his office. It's a 3/4 rear view with double diamond shock waves coming out of each engine. It's autographed by Kelly Johnson and Ben Rich. I know that if it ever turns up missing, I'll be a primary suspect.