The situation is that one system is using a Xeon E5-1650 6-core @ 3.2 / 3.8GHz and the other is running on an Xeon E5-1650 v2 6-core @ 3.5 / 3.9GHz.
To change the Xeon E5-1650 system to running a 3.5GHz base clock, it is necessary to buy and install a motherboard that can run the E5-16XX v2 processor. The motherboards can be identified by the Boot Block Date date in BIOS: the first version is 2011 and for the v2 second version, the date will be 2013) and then to buy and install a Xeon E5-1650 v2. If the system is a z420 or z620, changing the motherboard is quite easy: remove the GPU, carefully unplug all the power connections to the motherboard, turn the two large green retaining tabs 90 degrees, and slide the motherboard towards the front of the case, tilt and withdraw.
The Xeon E5-1650 v2 is interesting in terms of clock speed as it is one of the rare Xeons that may be overclocked, using the free Intel Extreme Tuning Utility (XTU). The others in this series are E5-1660 v2 and E5-1680 v2.
Using XTU is very easy; choose a multiplier and add voltage until the CPU is stable.
Keep in mind that overclocking will increase the CPU temperature and control of that temperature is the limitation on maximum clock speed. Two of the office systems- z620 and z420- are using E5-16XX processors that are overclocked to 4.3GHz on all cores, but this requires using the z420 AIO liquid cooler. Without the liquid cooler the highest all-core clock speed on both is 4.1GHz.
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