As far as speed goes, the first Blackbird (
A-12) was designed for
Mach 3.2, but has been unofficially reported to be capable of Mach 3.6. A variant (
D-21) has a published maximum speed of Mach 3.35. All other variants top out at 3.2 on paper, but pilots have reported reaching at least Mach 3.5 on sorties. Any faster than this, and the shock wave generated by the nose can narrow enough to enter an engine causing it to
unstart. That is, if an integral component doesn't
melt first.
Random facts:
When the SR-71 arrived at Kadena AFB in Okinawa, the locals took to calling it "Habu", after a poisonous snake found in the area. The nickname became associated with the aircraft and eventually the crew. SR-71 pilots that have flown operational sorties were awarded the Habu patch.
The fuel it uses was designed with a high flash point so as to not explode as the aircraft heated up in flight. In addition, a special system was developed that delivered the hottest fuel to the engines, and used the coldest fuel to cool the landing gear.
Speaking of landing gear, the tires also had to be designed to withstand the high temperatures the aircraft reaches. The rubber is laced with aluminum, and they are inflated with nitrogen.
The titanium used in building at least the first few Blackbirds was purchased from the Soviet Union.