How do I control the fan speed on the antec kuhler 620 water cooler

I have the same problem with my 620 except my fan rpm rarely reaches 1400 rpm. It usually runs 1380rpm. The cpu socket temp peaked at 72C while running Prime 95 for a couple of hours but the fan speed never changed from start to finish of the run. I'm running a Phenom II x4 960t unlocked to a X6 1600t O/C to 4.0Ghz@1.325v. Unlocking the cores disables the core temp reading so I can only read the socket temp. The socket temp on my motherboard is usually 10-12 degrees over the core temps from the readings I gathered before I unlocked the cores. I would like my core temps to stay the 50's and not climb into 60's. I have a couple of 4-pin PWM fans that I'm going to relocate and use in a push/pull configuration to see if I can get better performance. I'll move the 620's fan to a power fan header and use it as an intake fan and see if it actually hits the 2000 rpm it is supposed to.