1. Preheat oven to 350°. Place pecans in a single layer on a baking sheet, and bake 12 to 15 minutes or until toasted and fragrant, stirring after 6 minutes.
2. Beat softened butter and cream cheese at medium speed with an electric mixer until creamy. Gradually add 1 cup granulated sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition.
3. Combine whole wheat flour and next 4 ingredients; gradually add to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in bananas, toasted pecans, and vanilla. Spoon batter into 2 greased and floured 8- x 4-inch loaf pans.
4. Combine 1/4 cup all-purpose flour and brown sugar in a small bowl. Cut in peanut butter and 1 1/2 tsp. butter with a pastry blender or fork until mixture resembles small peas. Lightly sprinkle mixture over batter in pans.
5. Bake at 350° for 1 hour or until a long wooden pick inserted in center comes out clean and sides of bread pull away from pan, shielding with aluminum foil during last 15 minutes to prevent excessive browning, if necessary. Cool bread in pans on wire racks 10 minutes. Remove from pans to wire racks. Let cool 30 minutes.
Note: To make ahead, proceed with recipe as directed through Step 5. Cool loaves completely, and tightly wrap with plastic wrap. Wrap again with aluminum foil. Freeze up to 1 month.