Heavy bent-over dumbbell or barbell rows are still best for building an impressive back, but the rhomboid pulldown is a great finishing exercise for adding more volume without taxing you as much as the bigger movements.
Use a V-bar or close grip attachment and pull down to your sternum while flaring your elbows out at a 90-degree angle. Keep your trunk stable to prevent excessive rocking.
So you can squat 405 pounds and bench 315. Is that good? Does that make you strong? How do you compare to others? Find out if your lifts are decent, good, or great through Tim Henriques' handy little comparison chart.