Preheat oven to 350 degrees. Grease two 8x4 loaf pans. In a stand mixer, cream butter and sugars together until light and fluffy. Add in eggs and beat until mixed. Next, add vanilla, cinnamon and sour cream. Mix in flour, baking soda, and salt. Mash bananas in a bowl and stir in until combined. Pour batter evenly into two loaf pans.
In a small bowl, combine cinnamon streusel ingredients. Cut cold butter into the flour, cinnamon, brown sugar with a pastry cutter until coarse crumbs are created. Sprinkle streusel evenly over the batter in both pans and gently pat down. Bake 35-40 minutes, until toothpick comes out clean.