How fast is a fighter jet?

Most modern fighters can reach speeds of mach 2 or twice the speed of sound but rarely ever do so. Air engagements usually happen at 400 knots or so and acceleration is utilized for positioning more than anything. When needed this type of acceleration needs to happen pretty fast so a lot of power is needed. Then, as a byproduct of power comes speed. But accerating to and maintaining top speed seriously reduces the range of the aircraft because so much fuel is used to attain and maintain that speed.