The payload is small but is still capable of putting down a two legged threat and is nothing to sneeze at.
It may not be anything to sneeze at and it may be capable of putting down a two legged threat, but what is more likely to put an instant end to any threat; a 12 or a .410 given similar munitions? It is really that simple.
The closest test I know of is this one from the box of truth, and it isn't totally analagous due to it neing with a Taurus Judge and barrel length being a factor in creating velocity. http://www.theboxotruth.com/docs/bot41.htm
I would add that some are concerned with over penetration and collateral damage. Ask yourelf how much energy is delivered on target by 9 pieces of lead compared to 3, with both loads having the same total mass. I believe it is approximately the same. One difference is that if one of the 3 oversize pieces misses it is more likely to go through a wall and hit your neighbor. If one or more smaller pieces miss they are less likely to have the energy to reach the neighbor and if they did reserve energy is likely to be minimal.