Something to consider is the type of cooler. There is the Tube&Fin, which is the most popular because it is the least expensive. The other is what is called a Stack Plate style. In the tube&fin, the oil is routed through a steel tube in a serpentine fashion with the heat transfering to the fins. The stacked plate design routes the oil through small channels and transfering the heat to a series of plates. The big difference is how much surface area the oil comes in contact with and how fast the oil flows through the cooler. You can flow oil through a cooler too fast and not reduce its temperature much. On both accounts the stacked plate cooler is superior but 2 or 3 times the money.