Hi,
just to quickly pitch in with a particular hardware recommendation: The IPFire Mini Appliance supports 1 GBit/sec. throughput, even for IPsec (protocol-inherent overhead excluded), and is properly tested, with commercial support available. Plus, purchasing one will do the IPFire project some good… 
(Full disclosure: I am not related to or affiliated with Lightning Wire Labs, the company offering IPFire appliances and professional support, in any way.)
Thanks, and best regards,
Peter Müller