Preheat oven to 425°. Sprinkle potatoes with salt and pepper; bake, uncovered, in a greased 15x10x1-in. baking pan until tender, 40-45 minutes. Cool in pan on a wire rack.
Combine potatoes with next 5 ingredients. In another bowl, combine sour cream, mayonnaise and mustard; pour over potato mixture, tossing to coat. Refrigerate until serving.
