Sorry I don’t know much about the different 12 / 20 gauge offerings, or drums. If money is no object, here is a pricey, legal option. This is the USMC M4 shotgun.
http://www.benelliusa.com/shotguns/benelli_m4.php
Saiga12
Cons: Heavy with large mags. Your limited to 2 3/4” shells in the USA mags & drums; 3” fit into the mags, but will split them under fire. You need the Saiga factory 5 or 8 round mags to use the 3” shells. Mags and drums are expensive.
Pros: Have you ever shot a drum feed shotgun? OH HELL YEA!!!! Reliable and a blast to shoot.