Grease two 9x5 loaf pans. Set aside until needed. Cream together butter, 2 cups sugar, and eggs. Add milk, flour, and baking soda. Mix well. Put 1/4 of batter in each greased loaf pan. Mix in separate bow the 2/3 cup sugar and cinnamon. Sprinkle 3/4 of the cinnamon mixture on top of the batter in each pan. Add remaining batter to pans; sprinkle the remaining cinnamon topping. Swirl with a knife. Bake at 350 degrees in a preheated oven for 45-50 minutes or until toothpick tester comes clean. Cool in pan for 20 minutes before removing from pan. Excellent if eaten warm out of the oven but great toasted with a little butter or cinnamon butter.