Yeah APU2C4 performance is impressive.
I don't know who "achieves" 100mpbs via OpenVPN on an APU2C4, but I'd say something is a bit wrong there. Just for fun I clocked a Raspberry Pi3 that runs an openvpn aes-cbc-128 bridge (the other side being in a VM on a server). The Pi pulled a 4GB file averaging 75mbps... (cpu-bound on one core, local sink /dev/null)
I just wish OPNSense allowed bespoke opvn configurations, on that day I'd relieve quite a few VMs from running a tunnel endpoint. With AES-NI and VPN software that works, I expect no less than wire-speed openvpn tunnels on the APU2C4.