Preheat oven to 350 F. Beat butter and cream cheese together with an electric mixer until creamy. Add sugar gradually, and beat until light and fluffy. Add eggs, one at a time, and beat until blended. Gradually add flour and the next three ingredients to butter mixture, beating at low until just blended. Stir in bananas, pecans and vanilla. Spoon batter into two greased and floured 8-inch-by-4-inch loaf pans. Batter will be thick.
For streusel: Stir together 1/2 cup packed brown sugar, 1/2 cup chopped toasted pecans, 1 tablespoon flour, 1 tablespoon melted butter and 1/8 teaspoon cinnamon. Sprinkle mixture evenly over batter in pans. Bake for 1 hour or until a wooden pick inserted in the center comes out clean.
Bread may be shielded with aluminum foil during the last 15 minutes of baking to prevent excessive browning of streusel. Cool in pans on a wire rack for 10 minutes. Remove from pans, and cool an additional 30 minutes before slicing. For perfect slices, cut with a serrated or electric knife after cooling. Makes two loaves.