given that soviet air doctrine downplayed dogfighting in favor of ground control guided interception, i suspect that the MiG-25 would have been murder on most bombers, and would have been hard for western fighters to counter effectively if it avoided being sucked into a dogfight. with its speed if the initial exchange of missiles didn't take out the enemy, the MiG's would probably just put pedal to the metal to withdraw and come around for another pass once they were in safer airspace.