Lots of good questions, Louisiana Man -- but most above my pay grade. Bullet penetration and wound mass (by MacPherson's recipe) are about as far as I'm willing to venture into the morass of the stopping power debate.
Dunno! But the POI part could be easily tested -- especially if one of the bullets cut a cleaner hole so you could tell which hit where. As for "enhanced disruption," I suspect there might not be any. Some of Fackler's wound profiles show massive permanent cavities with pieces of "Detached Muscles" within -- but only for high energy rifle bullets with serious expansion, fragmentation or yaw. His only multi-projectile wound profile (#4 buck at 1350 f/s) shows no "Detached Muscles" and it looks to me that he intended to show the "Permanent Cavity" as only the actual path of individual projectiles. Maybe hard, sharp-edged wadcutters would lacerate stretched tissue where soft, round shot slips by. But in Clear Ballistic gel I never saw any evidence of that. Even when video clearly showed a beer can sized temporary cavity, the final wound tracks from two-projectile .38 and .44 WC loads looked like they were made with knitting needles.
Dunno this either. But MacPherson (in
Bullet Penetration) hypothesizes that there should be some "adequate" amount of wound mass required to incapacitate an attacker with a "non-vital" wound. He pegs this at about 40 grams based on a less-than-convincing argument involving the Thompson-LaGarde tests on beef critters in 1904. But MacPherson clearly states that if 40 grams isn't enough, then it might take a lot more to incapacitate a determined attacker.
For perspective, 40 grams of wound mass is about what you might get from the highly regarded .38 Special FBI load or the best 9mm JHPs. It's also about the same as a heavy .44 WC at modest velocity from a Bulldog without straining shooter or gun. A two projectile load of 150 grain WCs might gain 10-15% in wound mass at the expense of reduced penetration with increased recoil and wear and tear on the Bulldog. Again, if marginal penetration is the concern, a slightly rounded bullet shape (like Accurate Mold's 43-150M) solves that problem with even more wound mass.
I'm not sure about the "nervous reaction" part. But there can't be anything good on the wrong end of a cylinder full of two-projectile loads from a Bulldog. The total calculated wound mass from the cylinder full of .44 WCs shown below is about 220 grams -- enough more than the 160 gram wound mass from a 12 gauge slug to provide food for thought.