You can use a motion path… so their speed will be the same as an animated null for example.
physics -> air -> motion path.
Usual workflow is to create a light, rename it Motion Path 1. link it to a null and turn it off (so it wont affect your 3d layers).
now animate that null as you would.
tip: set the emitter position to the same start position of your null…and you can get a good idea of its motion.