Combine crumbs and butter; press into bottom and 1 inch up sides of a lightly greased 12-inch springform pan. Set aside.
Beat cream cheese at medium speed with an electric mixer until smooth; add 1 cup sugar and vanilla, beating until creamy. Stir in 6 egg yolks. Pour 2 1/2 cups mixture into prepared crust; set aside.
Add pumpkin pie mix and 2 eggs to remaining cream cheese mixture, stirring well; set aside.
Beat egg whites at high speed until foamy. Add remaining 1/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form and sugar dissolves. Fold into pumpkin mixture; pour over cream cheese mixture in crust.
Bake at 300° for 1 1/2 hours. Turn oven off, and run a knife around edge of cheesecake to loosen. Let stand in oven with door partially open for 1 1/2 hours. Remove sides of pan; cover and chill.
Beat whipping cream and powdered sugar at high speed until soft peaks form; spread on sides of cheesecake. Garnish, if desired.