What circuit would you be shooting at? You can use a 70-200 at every circuit, its just that at some circuits such as silverstone you would have to get creative with the shots you do.
I shoot at Lydden and a 70-200 is ample to be honest, have just bought a 100-400 and at 400 you are just toclose but at somewhere like Silverstone youd get some good head on shots etc with it.