Mix cookie crumbs and butter; press onto bottom of 9-inch springform pan.
Beat cream cheese, sugar and peanut butter with mixer until blended.
Add sour cream and vanilla; mix well.
Add eggs, 1 at a time, mixing on low speed after each just until blended.
Melt 4 oz. chocolate as directed on package.
Transfer 3 cups batter to medium bowl; stir in melted chocolate.
Pour over crust. Refrigerate remaining batter until ready to use.
Bake cheesecake 1 hour or until center is almost set, gently spooning remaining batter over partially baked layer in pan after 30 min. Run knife around rim of pan to loosen cake; cool before removing rim. Refrigerate cheesecake 4 hours.
Melt remaining chocolate; drizzle over cheesecake.