Prepare Crust: Mix together graham cracker crumbs, melted butter and sugar with a fork, until moistened. Press mixture onto the bottom of a 9 inch springform pan. Tightly wrap outside of pan with foil to prevent leakage when baking in water bath later. Bake crust 10 minutes. Cool completely in pan on wire rack.
Prepare Pumpkin Filling: In a large bowl, with an electric mixer on medium speed, beat cream cheese until smooth. Slowly beat in sugar until blended, about 1 minute, scraping the bowl often with a rubber spatula. With mixer at low speed, beat in pumpkin, sour cream, bourbon or vanilla, cinnamon, allspice and salt. Add eggs 1 at a time, beating just until blended after each addition.
Pour pumpkin mixture into crust and place in a large roasting pan. Place pan on oven rack. Carefully pour enough boiling water into pan to come 1 inch up side of springform pan. Bake cheesecake, 1 hour 10 minutes or until center, barely jiggles.
Meanwhile, prepare Sour Cream Topping: In a small bowl, with a whisk, beat sour cream, sugar and vanilla until blended. Remove cheesecake from water bath, leaving water bath in oven, spread sour cream mixture evenly over the top. Return cake to water bath and bake 5 minutes longer. Remove cheesecake from water bath to wire rack, discard foil. With small knife, loosen cheesecake from side of pan to help prevent cracking during cooling. Cool cheesecake completely. Cover and refrigerate cheesecake at least 6 hours or overnight. Remove side of pan to serve. Garnish with a dollop of whipping cream.