Two things happen when you lift heavier - you burn more calories and you burn more calories longer after the lift. In other words, lifting 200 pounds 5 times will burn more calories than lifting 100 pounds 10 times, even though the workload is the same. This is because of the way your anaerobic system is taxed, changes to your heart rate, the way the body accumulates what is known as "oxygen debt" and how the body pays off that debt using EPOC (exercise post-oxygen consumption).
So if your goal is to burn more calories, a super-circuit at a quicker pace will actually burn less calories. Lifting hard and heavy will burn the most calories during the lift and keep your metabolism elevated the longest.
