Help with High CPU Usage in OPNSense VM inside Proxmox

[saluteferux]

Hi everyone,
I'm experiencing an issue with high CPU usage in my OPNSense VM running inside Proxmox and could really use some help.
Setup Details:

    Host Configuration:
        Proxmox Host
        64 GB RAM
        Intel i7-8700 (mitigations=off)
        IOMMU enabled (iommu=on and iommu=pt in /etc/kernel/cmdline)
        Proxmox installed on SSD NVME in ZFS RAID0
    VM Configuration:
        OPNSense VM
        8GB RAM
        1 socket, 4 CPU threads (using host cpu type, testing with others doesn't change anything)
        Passing through 4 ports of Intel I226V 2.5GbE. PCI-E is on in the settings of pci devices.
        Q35, OVMF (UEFI)

Issue:
When I run a speed test, downloading at speeds of 2.1 Gbps to 2.5 Gbps, Proxmox reports 80-100% CPU usage. However, inside the OPNSense dashboard, the CPU usage is reported as 5-20%. (Same tested with pfsense)
I’m trying to understand why the CPU usage is so high on Proxmox.
Things I've Tried:

    Ensured that IOMMU is enabled and configured properly.
    Verified that CPU mitigations are turned off for performance.
    Tested with Pfsense
    Tested OpenWRT and the CPU Usage doesn't go above 10-15% at full 2.5Gb speed so this is a problem with the senses...

Questions:

    Why is there such a discrepancy between CPU usage reported by Proxmox and OPNSense?
    Is there anything I can do to optimize or reduce the CPU usage on Proxmox when running high-speed network tasks?

Any insights or suggestions would be greatly appreciated!
Thanks in advance!