Sometimes you have to take "Top Speed"s of fighters and bombers with a grain of salt. These speeds are at that particular aircraft's ideal altitude, that is, the plane will be slower at all other altitudes than the rated speed. The B29s principal advantage was its ability to fly fast at very high altitude when some Japanese fighters had already "run out of breath" so to speak.
Also, if you're talking about fighters intercepting bombers, a typical (or smart) fighter pilot won't "tail chase" a bomber formation going such-and-such mph and try to hammer them from behind, rather will attack at an angle, head on or primarily from above in a dive.