In a mixer bowl, blend sour cream, mustard, pepper, salt, garlic powder, and Worcestershire for 2 minutes at low speed. Add mayonnaise. Blend 1/2 minute at low speed and 2 minutes at medium speed. By hand, crumble the cheese into the mixture. Blend at low speed no more than 4 minutes. Refrigerate 24 hours before serving.
For chunky salad dressing, reserve some of the blue cheese crumbles to stir in after blending.