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.
I agree. Heavy birdshot as the first round in the magazine, followed by buckshot if the first round doesn’t solve the problem.
My cop friends tell me number 4 is what their SWAT team prefers inside of residences. Best compromise of spread and penetration.