Encryption is what kills you on VPN.
It requires horsepower.
In it's class the FVS336Gv3 offers the fastest theoretical throughput so it's a good choice but the cons are it's not as feature rich as other offerings in its class. EDIT: VPN throughput is just shy of 80 theoretical. You might see 60, ish.
If you have a relatively new PC hanging around that you can dedicate to the task you might be better served by going with pfsense.
https://www.pfsense.org/
You can get up to 100mbps with a 1ghz CPU, more if you go with a better spec box and PCI-e NIC.
https://www.pfsense.org/hardware/#requirements
pfsense is open source so you can just download the install and off you go.
https://www.pfsense.org/download/