Right full answer is, it depends on what you are shooting and where you a standing. Motorbikes or cars.
With a crop camera then you'll have plenty of reach with either 100-400 or 70-200 with 2x. The 70-200 would give you slightly more flexibility but I never found an issue with the 100-400 and low light and you have slightly more useable range.this was with my 50d and the 7d is a much better camera.
Just looked through my last shots, Some places you'll need long, other such as inside Druids you could be down to 50mm