Sophos IPSEC using Sophos Connect Link Speed 100mbps

Interface Speed is not related to the openvpn speed. 

Openvpn itself is limited by the technology of openvpn. You will not get to top speed with one client: https://community.openvpn.net/openvpn/wiki/Gigabit_Networks_Linux

As the internet uses MTU1500, you will be crushed by the overhead. 

Makes sense, its more than that 100mb/s threw me thinking 100mb would be the max achievable as the sophos interface indicated, I'll have a fiddle with the different negotiation options see if we can get the best bang for buck out of it, realistically its 50 odd users so even if they were all getting 100mb/s on the 10gb line thats better than the 1gb line they had previously just would be nicer to get their local speeds in transfer where possible.

I'm assuming the restrictions are also present when using SSL VPN?

Makes sense, its more than that 100mb/s threw me thinking 100mb would be the max achievable as the sophos interface indicated, I'll have a fiddle with the different negotiation options see if we can get the best bang for buck out of it, realistically its 50 odd users so even if they were all getting 100mb/s on the 10gb line thats better than the 1gb line they had previously just would be nicer to get their local speeds in transfer where possible.

I'm assuming the restrictions are also present when using SSL VPN?

Yes, but some users get better SSLVPN performance based on the GCM Encryption method. 

Best get to some testing I think, thank you for your help.