2 x thoughts:
1) You can add spacers to the Magpul stock to increase LOP. If the factory stock is too short for you, the need to mount a longer stock might be an issue for you.
2) The Benelli M4 is gas operated, and is not the same as the inertia-operated M2, so this particular comparison is not apples:apples as compared to the M2.
The M4 is certainly an awesome shotgun in it's own right.