I use a D945GCNL board. Not sure how the BIOS differs with your motherboard. In BIOS under Advanced --> Boot Configuration, You have some thing called CPU Fan control and Sytem Fan control. Disable both and your System as well as CPU fan will be running almost their maximum speeds. You can use the Speedfan utility to check the Fan speeds in Windows.
When you disable the sytem fan control in BIOS your LED Fans will run with the LED On with their maximum speed.
Hopes this helps you a bit.
My CPU Fan runs @ 2380 rpm and System fans both run @ 2700 rpm