I've read thread upon thread upon thread over the years regarding break-in. Each with their valid points. Me personally, I like to follow the 1k mile train of thought while not letting the RPM's sit at one rate for too long a period of time and just being generally real easy on the throttle. Did it with my last 2 bikes and my current car and never had any issues. I'll change the oil at 1k and then it's game on in my opinion.
According to the 2011 Mustang GT owner's manual, very little break-in is required for these cars. I believe it said that (almost exactly) and said to vary highway speeds for the first 1000 miles. That's it (if I recall correctly).