Help Troubleshooting Sluggishness on R710 II Running Windows Server

Windows Server on a well equipped R710 II is very slugish as though something was taxing the box:

• When typing the text lags behind the keystrokes
• Downloading & installing 3 updates (KB4034661, KB4035631 & KB3186568) took well over 3 hours
• Enabling RSAT & Hyper-V took about an hour

Yet Task Manager and Resource Monitor don't show the CPU, RAM or Network being taxed.

I've been working on this for a few days now and I'm nearing the end of my rope:

• Switched to UEFI & installed Server 2012 R2 bootable media not LC with just the keyboard, mouse and display attached (no network not even in mgmt port)
• Had NOT upgraded firmware before doing this so I thought that might be contributing to the performance problem.
• Upgraded everything via LC and reinstalled the OS - no change.
• Thinking it might be 2012 R2 specific, I installed Server 2016 (don't chastise me about that please), via bootable media - no change.
• Switched from UEFI to legacy BIOS reinstalled the OS - no change
• Ran the extended tests and aside from two old errors (The storage SAS A cable is not connected, or is improperly connected. & Fan 5 RPM is less than the lower critical threshold.) all was fine.
• Ran the memory test checking every option (e.g.: mats, march b, ecc etc) and after 4 passes everything was fine.
• Removed two Emulex / EMC LightPulse LPe12000 adapters and a single-port Intel gigabit NIC - no change.
• Sluggishness is seen both physically at the terminal, via RDP and in child VM's
• Removed all modules keeping track of the DIMM slot each module was removed from
• Re-installed 6 modules back into their original DIMM slots: A1, A2, A3, B1, B2 & B3 (satisfying the 're-seating' of memory) - no change
• Removed modules A2, A3, B2, & B3 leaving just 2 total in A1 & B1 - slowness persists
• Removed 7 of 8 Dell 146GB 15.2K Savvio SAS drives (in RAID10 config) keeping track of drive position
• Re-initialized the remaining drive & reinstalled the OS - no change
• Removed the SAS drive, installed & initialized a single consumer grade SATA drive and reinstalled the OS - no change

At this point, it doesn't appear to be hard drive specific but at this point I'm thinking possibly:

• H700 controller
• RAM module(s)
• DIMM slot(s)
• CPU memory channel(s) - thus bad CPU(s)
• something else altogether?

Aside from that, I really don't know where to go from there so I'm reaching out for some guidance.
Anything you can think of or recommend would be greatly appreciated.

Server Stats:

• Dual E5649's
• 192GB - 12x16GB 2Rx4 PC3L-10600R 1.35V in Optimizer mode
• 8x Dell 146GB 15K SAS drives on an H700 in RAID10