We had made ssl and ipsec vpn tunnel on gigabit interfaces and then measured throughput. It was less than ~130 Mbps.
Who knows does Astaro limit ssl or ipsec vpn tunnels throughput?
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With the SSL VPN, did you change the protocol to UDP instead of TCP and select Compression on the 'Advanced' tab?
With IPsec, that sounds like an MTU problem.
Cheers - Bob