You can use a three pin to connect them directly to the MB header and the fan (speed) will show up being monitored by the MB. Or you can use the 4 pin molex and run them directly from the psu. With six you can even chain connect them together from a 4 pin molex lead to the psu. You can bring a lot of fresh air into the case for the CPU fan to cool with. Use some for intake and some for exhaust to create airflow throughout the case and across the MB. 120mm are the way to go.