Stir together first 4 ingredients in a large mixing bowl. Add eggs, sour cream, and oil; beat at low speed with an electric mixer 30 seconds or just until moistened. Beat at medium speed 2 minutes.
Pour 4 cups batter evenly into 2 greased and floured 8-inch round cakepans. Pour remaining 3 cups batter evenly into 2 greased and floured 6-inch round cakepans.
Bake 6-inch layers at 350° for 20 minutes and 8-inch layers at 350° for 25 minutes or until a wooden pick inserted in center of each layer comes out clean. Cool in pans on wire racks 10 minutes. Remove from pans, and cool.
Note: Use a 15- x 10-inch or 16- x 12-inch jellyroll pan for Small Tiered Cluster Cakes and Bridesmaid Baby Cakes. Bake at 350° for 20 minutes or until wooden pick comes out clean.