A stock M3 is a very quick car but it's severely hampered by its soft suspension, narrow wheels, and lack of camber.
With a few basic modifications - stiffer springs and better shocks, camber plates and wider front wheels and tires, the M3 will annihilate a Boxster in terms of numbers...
... but the Boxster will be more rewarding and more fun to drive. And it sounds much better.