Beat butter and cream cheese at medium speed with an electric mixer until creamy. Gradually add sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
Combine flour and next 3 ingredients; gradually add to butter mixture, beating at low speed just until blended. Stir in bananas, pecans, and vanilla. Spoon batter into 2 greased and floured 8- x 4-inch loafpans.
Combine 1/2 cup plus 1 tablespoon flour and brown sugar in a small bowl. Cut in 1/4 cup butter and peanut butter with a pastry blender or fork until mixture resembles small peas. Sprinkle mixture evenly over batter in pans.
Bake at 350° for 1 hour or until a long wooden pick inserted in center comes out clean and sides pull away from pan, shielding with aluminum foil last 15 minutes to prevent browning, if necessary. Cool bread in pans on wire racks 10 minutes. Remove from pans, and cool 30 minutes on wire racks before slicing.