Preheat oven to 350. Crushed graham crackers and mix crumbs thoroughly with 1 1/4 sticks butter and 6 Tbsp.. sugar. Put mixture in springform pan, pressing evenly onto bottom and up side of pan. Bake til golden brown, about 8 to 10 minutes. Remove from oven and cool on rack
In large bowl, using a hand blender or whisk, beat cream cheese and peanut butter til smooth. Add 3/4 cup sugar and 1/4 cup brown sugar and beat til fluffy. Slowly add eggs and 2 tsp. vanilla and blend.
Pour mixture into crust.
Cut two large pieces of foil. Place springform pan in center of foil and fold foil up the sides. Place in larger roasting pan and add enough water to come up 1 inch on the outside of the springform pan. Bake til golden brown, about 1 1/4 hours. Remove and cool in refrigerator uncovered for at least 6 hours.
To make banana layer, slice bananas 1/2 inch thick. Put remaining 1 stick butter and remaining 1/2 cup brown sugar in large pan over medium heat. Whisk til sugar and butter melt and mixture is smooth and caramel like, about 3 to 4 minutes. Add banana slices to pan in single layer and cook for 2 minutes, turning once. Using a fork, carefully transfer banana slices to top of cheesecake, arranging in an even layer. Return to refrigerator.
Put whipping cream, remaining 2 tsp. vanilla and powdered sugar in mixing bowl. Using an electric hand mixer, beat cream til stiff.. Spread whipped cream on top of bananas. To garnish, grate chocolate over top.