Poor overall performance?

Solution
RAM - "3 of 4 slots used; 24GB DIMM DDR3 1066 MHz clocked @ 533 MHz"

I'm guessing that your system is being forced to run in single channel mode. Suggest you try two RAM slots to see if this improves. You may need to check dual channel enabled in BIOS. With two sticks it should run in dual channel mode. Be sure to choose two RAM slots of the same colour!!

Apparently the RAM and mobo are both 1866Mhz capable, but I'm not familiar with these, so I recommend setting BIOS to auto, and just look around within BIOS to see if you can spot the RAM at 533 / 1066 / 1866. Perhaps use HWiNFO64 to see the CPU and RAM frequencies.

This should improve your RAM benchmark, and you have the option to add a 4th stick and have 32GB in dual channel...
RAM - "3 of 4 slots used; 24GB DIMM DDR3 1066 MHz clocked @ 533 MHz"

I'm guessing that your system is being forced to run in single channel mode. Suggest you try two RAM slots to see if this improves. You may need to check dual channel enabled in BIOS. With two sticks it should run in dual channel mode. Be sure to choose two RAM slots of the same colour!!

Apparently the RAM and mobo are both 1866Mhz capable, but I'm not familiar with these, so I recommend setting BIOS to auto, and just look around within BIOS to see if you can spot the RAM at 533 / 1066 / 1866. Perhaps use HWiNFO64 to see the CPU and RAM frequencies.

This should improve your RAM benchmark, and you have the option to add a 4th stick and have 32GB in dual channel mode. It is best to use identical RAM model numbers in all situations. Address the RAM issue and see how the rest of the system responds in the benchmarks when RAM is running in dual channel mode.
 
Solution