Speed records are usually done with specially prepared prototype aircraft. The F-15's many records (some taken from the MiG-25) were done with a stripped down experimental prototype called the Streak Eagle. They even stripped the paint of it. It is now in the National Museum of the USAF.
The MiG-25 is limited to about 5 minutes at mach 2.84, 20 minutes at Mach 2.6 and can fly a whole mission at mach 2.4 (though it will be a short one). When flying at Mach 2.84 the canopy heats up to about 70C so the space suit like pressure suits the pilots wear are vital. The MiG-25P and MiG-25BM carries their R-40 and Kh-58 missiles externally and can hit Mach 2.83 while doing so thanks to the surplus thrust provided by the Tumansky's at that speed. The weapons have a special coating to make them withstand frictional heating.
The MiG-25 was redesigned into the MiG-31 to counter NATO's switch from high-altitude to low-altitude penetration.
The MiG-25 wasn't the super-fighter the west thought it was, but it was a pretty darn good interceptor. It was also the only aircraft in the Iraqi air force that managed to shoot down a coalition jet.
"17 January 1991. On the first night of the war, two F/A-18's from the carrier USS Theodore Roosevelt were flying outside of Baghdad when two Iraqi MiG-25s engaged them. In the beyond-visual-range (BVR) kill, one of the Iraqi MiGs piloted by Zuhair Dawood, fired an R-40 missile. The missile impacted Scott Speicher's jet head on when he was travelling Mach 0.92. The impact sent him spiraling downwards and most people believe he died on the impact of the missile.
Two IRAF MiG-25s fired missiles at a group of F-15Cs escorting a bombing run in Iraq (which were evaded by the F-15s). The F-15Cs give chase, but were forced to give up when the MiGs outran them. A total of 10 missiles were fired at the MiGs."
"5 January 1999. A group of four Iraqi MiG-25s crossed the no-fly zones and sparked a dogfight with two patrolling F-15Cs and two patrolling F-14s. A total of six missiles were fired at the MiGs, none of which hit them. The MiGs then bugged out using their superior speed."
So the age-old fighter pilot's motto "speed is life" seems to ring true even in today's world of advanced sensors and weapons.