Performance Issues with my 7810

I own a Precision Tower 7810 with dual Xeon 2640 V3 CPUs. 

Also have an OEM computer with an i7 3930K Cpu. 

When I buy a computer I always test the 3d rendering performance and compare it with other devices to ensure everything is ok. I first noticed that this OEM 3930K was working slower than it should, and upon a thorough search with a free software called Hardware Monitor, I realized that the cpu runs about %30 lower than its maximum frequency during 3d rendering. It turns out the official Intel fan that is sold together with this cpu doesn't cool this cpu adequately. CPU throttling slows down the system when the CPU temp reaches its maximum. I changed the CPU fan with a large one and the CPU started running at its max, decreasing the render times.

Now I have similar values with my Dell Workstation. I see 3392mHz in CPU max speed, but it often runs at 2793mHz during rendering, which is a 600mHz loss. I entered the BIOS setup and maxed the fan speeds. Dell workstations' fans seem to be more than enough looking at the noise they make but it doesn't help increase the frequency.

Any ideas about the reason of this frequency loss? Is there a setting that unleashes the power of my cpus?

Best regards