It depends if they are going down a runway it would be good to have a faster shutter speed but 1/1000th of a second is still probably over kill. Usually at runway shows the lighting is very poor so you will need to use a flash which will limit you to your flash sync speed probably around 200th to 250th of a second depending on your camera. You can you faster shutter speeds with your flash if it supports high sync speeds but you loose a lot of output from your flash when doing this. I think 200th - 250th of a second should be good enough to freeze motion in most situations.
For your particular shoot something around 100th of a second would work pretty well and should freeze any small movements the model may make, you can probably get away with an even slower shutter speed.
Each situation will be different if they are posed shots generally you don't need shutter speeds that fast. I would still however keep your shutter speed faster then the focal length you are shooting at to reduce camera shake. If you need to freeze the action of a model such as jumping in the air the shutter speed will need to be faster thus limiting you to what aperture you can use depending on the light you have to work with.
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