The next levels of police.....

[Porsche-AG]

How about a Lamborghini Gallardo Polizia for level 7? Follows the pattern quite well, and it's actually a real police car, but there could only be 1 Gallardo as there is only 1 in real life. Click here for image: http://upload.wikimedia.org/wikipedia/c ... olizia.jpg

And that Mercedes CLS police is tuned by Brabus if I'm not mistaken.

Level 10 could be this London Murcielago LP640 Police: http://www.sybarites.org/wp-content/Screenshot_1_10.jpg