Bake potatoes in preheated oven until easily pierced with a fork, about 1 hour. Allow to cool for 10 minutes. Do not turn off oven.
Meanwhile, cook bacon in a large deep skillet over medium-high heat until evenly browned. Drain, crumble, and set aside.
Slice potatoes in half lengthwise and scoop flesh into a large bowl; save skins. Mix in sour cream, milk, salt, pepper, 1/2 cup Cheddar cheese, and half the green onions into potato flesh. Blend with a hand mixer until creamy. Spoon potato mixture into potato skins. Top each with remaining 1/2 cup Cheddar cheese, 4 sliced green onions, and bacon.
Bake in oven until filling is hot and cheese is melted, about 15 minutes.