Hydraulic Fan Drives for reduced fuel consumption, increased available power

Hey all, I am doing research on Hydraulic Fan Drives, anyone ever done a conversion on their machine, I have read a couple of case studies where they state a 5-14% decrease in fuel consumption, increased engine power available for other functions because you do not need to run the fan at high rpm constantly. On larger engines the HP required to drive the fan is large, upwards of 40HP. In one case study, they converted a haul truck, the unit got a 14% increase in fuel mileage and increased speed, which meant they did more fill dump cycles per shift, and reduced particulate emissions. They conversion was paid off in about 3 months, after that is was making money for the company. Any thoughts??