For highway use or traffic patrol of areas where the officer spends a lot of time just driving the roads, especially away from the city and in ares of 55 mph and faster limits, I think that the 5.0 Mustang is the best bang for the buck out there.
The cops will get a 400+ hp vehicle that's capable of running some very high speeds very safely, for not a whole lot more money than a regular performance patrol car like the ones Chrysler is building for most of the departments. The insides of the Mustang aren't that much smaller than the 4 door Dodge's that many departments up here are running, and you get a WAY better performing car.
My old man finished his career off in traffic back in the late 90's, and he drove a notchback 92 Mustang GT for the last year, and loved it. The RCMP here in Canada did away with them though around that time, and haven't done much in the way of high speed interceptor type police vehicles since. This would be a great time for them to start again, with the 2012 or 13 Ford GT's.