There is no autoloader as fast as a Model 12 in the hands of someone who knows how to shoot a Model 12. The simple reason is that the Model 12 has no disconnector. All you have to do is hold the trigger back and shuck the cob. With practice, you can do it fast and accurate.
That feature isn't unique to the Model 12. It is also found on the Winchester Model 97, Ithaca Model 37 (not sure about the Remington 17 and 31), Stevens 520 and 620, and some of the "house" brand guns based on these designs.