Stir together first 6 ingredients in a large bowl until blended, and stir in cheeses.
Heat an electric griddle to 350º or a nonstick skillet over medium-high heat. Spread 1/3 cup cheese mixture on each of 4 bread slices. Top evenly with tomato slices and remaining 4 bread slices. Brush one side of sandwiches evenly with 1 tablespoon melted butter.
Spray hot griddle or skillet with cooking spray. Place sandwiches, buttered sides down, on griddle or in skillet. Brush tops evenly with remaining melted butter. Cook 2 to 3 minutes on each side or until golden. Serve immediately.
Note: For testing purposes only, we used Kraft 2% Milk Sharp Cheddar Cheese and Cabot 50% Light Vermont Cheddar Cheese.
Note: Nutritional analysis per 1/3-cup pimiento cheese: Calories 125 (58% from fat); Fat 8.1g (sat 4.9g, mono 0g, poly 0g); Protein 11.2g; Carb 4.5g Fiber 0.2g; Chol 24 mg; Iron 0.2mg; Sodium 332mg; Calc 271mg.