In small bowl, mix mayonnaise and dressing. Spread on one side of each slice of bread. Top each of 4 bread slices with turkey, bacon, tomato, cheese and remaining bread slices, mayonnaise mixture side down.
Spread butter on one side of each sandwich. In 12-inch skillet, place sandwiches, butter side down. Spread butter over top of each sandwich. Cover; cook over medium-low heat 6 to 8 minutes or until bottoms are golden brown.
Turn sandwiches; cover and cook 5 to 6 minutes longer or until bottoms are golden brown and cheese is melted.