I know a few guys who swear by tungsten #9's for turkey out of a 410 shotgun. Guys are whacking geese with 410's and 28 gauges shooting #7.5 or #8 tungsten at distances formerly reserved for 10ga magnums shooting BB's or T-shot. True tungsten shot is 50% more dense than lead and the smaller sizes seem to pattern very well.
I've found some videos of guys shooting 1 1/2oz of tungsten BB sized shot at 1250 FPS into a gel block at 25 yards and getting around 16" of penetration with BB's (18 caliber). He also tested lead BB's which got less than half the penetration the tungsten ones did. A 1 1/2 ounce load of tungsten BB's contains roughly 47 pellets. So you're talking about 47 individual projectiles, any one of which can hole the vitals of most any person, at any angle. It appears tungsten BB's penetrate roughly the same or better as #1 buck however you could shoot ~40 (assuming a 2 3/4" 1.25oz load to be comparable) BB's with each pull of the trigger versus 15 with #1 buck.
Throwing the $4-8 a round tungsten shot costs aside, what would it take for you to consider stoking your defensive shotgun with tungsten loads? If Federal came out with a Flite control tungsten BB load tomorrow that patterned as good as the vaunted 8 pellet 00bk load, would you break out the credit card?