At close range (across a room), not necessarily. The birdshot will not have had a chance to spread out, and will hit as one mass. And the doctors will NOT have much luck digging out all those little pellets.
With only 3-4 inches of penetration in gelatin, I think #8 is not enough. A winter intruder with a heavy coat etc, would be knock down with minor penetration. It would feel like he got hit in the chest with a 95mph baseball and may temporarily incapacitate depending on the size of the guy or gal.
I would recommend at least #4 birdshot.