Degraded Speed Ghost

[juicemain]

At a glance:

Internet connection speed:
    1gig, usual speeds 940 mbps down / 940 mbps up
Temporary slowed speed state:
    ~700 mbps down / ~50 mbps up , (all pings/ latency stay generally consistent no degredation)
Triggers:
    Multiple, the one I found for testing was playing the video game Overwatch while doing an Ookla speed test in a web browser
Temporary fixes:
    Rebooting the router usually leads to a normal speed state most of the time, will revert eventually to the degraded speed state, which will eventually revert back to full speed overtime itself oscillating back and forth.

Degraded speed state DOES NOT occur on the ISP provided router solution, Calix U6 router.

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Hardware:

Systems:
Lenovo ThinkCentre m720q tiny (original system)
Dell OptiPlex 7070 SFF (second system)

NICS:
ULANSeN Dual-Port PCIe card (Intel 82575/82576 chipset)
NICGIGA 4-port i350 card (Amazon white-label)
Genuine Dell I350-T4 (4-port, used in both m720q and 7070)

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Timeline of troubleshooting steps taken:

(on Lenovo m720q tiny)
Multiple fresh installs of latest Opnsense
Disabled hardware offloading
Set tuneables
Observed pause frames and link flaps
Replaced original Ulansen 82575/82576 card with NICGIGA i350 4-port card
Tried multiple third-party PCIe risers
Isolated WAN/LAN port assignments on the multi-port cards
Removed internal wi-fi card
Scoured every possible BIOS setting in regards to PCIE slots and power management
Implemented FQ-CoDel traffic shaping
Isolated all network components down to PC -> m720q OPNSENSE router
Sourced genuine Dell I350-T4 with proper m720q low profile bracket
Checked ethernet cables

(on Dell Optiplex 7070 SFF)
Migrated to Dell Optiplex 7070 SFF with native PCIe slot
Retried all tunables
Installed and tested pfsense
Tested double NAT (7070 behind ISP router)

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Synopsis:

This ghost persists across different hardware, OS, and configurations.  I believe that I have isolated the issue either down to the PCIE bus / NIC itself, the Intel chipset igb drivers, and/or Freebsd itself.  I am an amateur, and this is for a home network setup.  If I'm missing anything glaring, please excuse.  This has been my last resort to come to the forums for this issue.  I'm sick of talking to an LLM.  I'm sure this is usually a place for enterprise issues, but thank you in advance.  You're my only hope lol.  Any and all suggestions appreciated.  Has anyone else ever had any issues like this when using a desktop PC as an opnsense machine?  Is it recommended that I move on to dedicated hardware? 

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Next steps:

1. Ordered a realtek chipset nic to tryout different drivers
2. WIll move to Protectli hardware next with soldered nic instead of pcie nic.