Are you using SSL or IPSEC VPN? SSL is rated to 120Mb/s but IPSEC is 800Mb/s

Neither, Wireguard. That's limited to 80Mb/s at the moment. 

It's worth noting that even with IPSec, if it's a NAT-T connection on the far end that's not hardware accelerated either and so limited to 120Mb/s too. For example, if you're using a Public VPN company like NordVPN, that'll be using NAT-T.