It is disturbing if it's 3M or similar material.
Check out this article: http://www.automotivearticles.com/Clear_Bra_3M.shtml
The author shot a pellet gun against his mirror (with and without film) from 10 meters at 280mph, and there was no paint damage when film was applied.
If you're getting paint damage from rocks at 60mph, something is seriously wrong with your film.
Maybe it was that and the M3 was spinning his tires, which may have increased the force of the impact?