My opinion comes from putting my M4 with mount/light, and an M2 with the same barrel length, same mount/light on a scale. The M4 was a whole lot closer to 2lbs heavier than 1lb heavier.
Yes they M4 comes in several models. But not counting the SBS (or fixed choke, removable choke, silly choke ), from the trigger forward they're exactly the same.
I have ever so briefly toyed with knocking the sight off the M4 and having a vent rib added, but that would be stupid money for a gun I'm not in love with.
And you can't get into a pissing contest with me, because I don't really care. Certainly nothing to win or lose, no minds to be changed, no different outcome even if they did.