Something else to consider - if fighters, using reaction drives can zip and zoom faster than anything else, how is it that a missile, whose mass is taken up by a seeker, a warhead and the engine, can't go faster than a fighter?  Missiles have no human occupant to worry about silly things like G-compensator, no need for a fusion reactor, no need for armor, no need for any extraneous mass.  And a reaction engine has a specific energy output, so more energy and less mess = faster object.