Struggling with 10 Gb LAN performance on bare metal instal. I7 6700

I7 6700 with 16 GB of RAM I225 (WAN and optional interfaces) X520-DA2 ( LAN and parent to VLANs)

On a fresh install with no extra packages or tweaks other than selecting intel quick assists for hardware acceleration and installing the OPNsense iperf3 package, I am unable to achieve anything close to 10 Gb throuput on my LAN interfaces with iperf3.

When I run iperf on my LAN interface and use a 10Gb client on the same network segment, I see about 4.3 to 4.4 Gb/s throuput. No NAT should be occurring.

I enabled RSS using the OPNsense performance guide, and this boosted me to about 5.5 Gb/s in the same scenario.

I then enabled checksum offload and this boosted me to 5.9 Gb/s.

What gives? I have seen others report zero issues being able to achieve 10Gb line rates with lower end hardware.