What do you use for creating the traffic?
I have pfSense 2.6.0-RELEASE (FreeBSD 12.3-STABLE) running on Proxmox VE 7.3-3 with multiple VirtIO NICs and two vCPUs (Intel Core i3-10100).
When running iperf3 between two FreeBSD VMs on different subnets/VLANs, I get 2.61 Gbps on average with peaks over 2.83 Gbps.
When running iperf3 between two FreeBSD VMs on the same subnet/VLAN, I get 4.36 Gbps on average with peaks over 4.64 Gbps.
Both VMs have one vCPU (also Intel Core i3-10100) and a single VirtIO NIC.
The Hardware isn’t really comparable, but I could of course test this with two of my HP T620 Thin Clients.