In a small bowl, whisk together the sour cream, buttermilk, mayonnaise, red wine vinegar, olive oil, sugar, garlic, salt and pepper. Stir in the crumbled blue cheese. Refrigerate at least 4 hours, preferably overnight.
To serve the salads, place a wedge of lettuce on a plate and drizzle with blue cheese dressing. Sprinkle tomatoes, red onion, blue cheese, and bacon over the top. Repeat with remaining wedges. Serve immediately.