A buddy of mine recently traded into an M3. He loves the gun, but the stock is just too damn long. In our research, we have found that there are very few aftermarket stock options for the M1/M2, and virtually none for the M3. Sad, really.
I've not quite stepped into "the big leagues" of Benelli ownership, but I do have a SuperNova tactical 18.4" barrel 12ga. that I absolutely love. It's my HD shotgun but I can still shoot clays with it out at the Indiana Gun Club. It's a little more challenging, but still a lot of fun! They make outstanding shotguns IMHO, I'm still eventually going to buy an M4 once I have some more debt paid down.