LOL! fighting SAm's with heat seekers? Im sure they would see a IR signature from a SAM but they are tipicaly much faster than heat seekers. It would be pointless to try shoot one down unless your flying straight into one wich would rather increase the odds of being hit than actualy fire the missile successfuly in time.

Remenber at mach 4+ all fighter airborne radars cant see anything so you would have to cue it visualy, its another limitation you have.

Typically you can expect one to be coming straight at you in most case yes - in which case the speed is adequate - its just whether it can get a lock and hit. You also need a good launch warning detector to tell you its coming because I cant believe eyes are good enough in a lot of situations.

I would have thought its possible that the missile would create a lot of heat through friction as it goes through the air at such a speed.

Is that true of all radars about objects faster than Mach 4 then? How does the missile avoid electromagnetic waves traveling near the speed of light?

Dec 3/07: During a test at White Sands Missile Range, an Air National Guard F-16 test aircraft from the ANG-Air Force Reserve Command Test Center in Tucson, AZ launches an AIM-9X airframe with the NCADE seeker at a boosting Orion sounding rocket. The official test objective was to demonstrate successful imaging at close range, but the missile went on to destroy the target. A second AIM-9X launched from White Sands Missile Range observed the intercept through its seeker; the US Missile Defense Agency says that it was also on a trajectory to intercept the Orion rocket.

Future testing will involve the missile's divert and attitude control (DACS) system, intended to give it the maneuverability it requires against such fast-moving targets.

Source