On the server side you could use one of the SG1000's as only a openvpn server..
Client(1) > – switch -- > wanrouter(3) > internet > wanrouter(4) > -- switch -- > SQLserver(6)
^ ^
| |
sg1000(2) sg1000(5)
So client could still use its wanrouter as the default gateway.
And the client(1) or the wanrouter(3) could then configure a extra route to the sg1000(2) when it wants to connect to the sql-server..
Then the sg1000(5) could be using outbound-natting to translate traffic from its vpn-clients to its own ip and the company network would need no changes at all.. But sql-server and other logfiles would show all clients connecting with sourceip of the sg1000(5).
Or instead of using outbound-net the wanrouter(4) or SQLserver(6) would need a route for the lan-network of client(1) to point to sg1000(5)..
Or you could install regular openvpn clients on the client pc's, (use openvpn export package from pfSense to create its config and possibly a Windows installer.) And not use the sg1000(2) at all..
It all depends on what you want want/need ;). usually pfSense becomes the edge router of the network, but if you want to push decent bandwidth, and also run VPN's over them the sg1000's might not have the processing power (ive never seen one in action.).. Also maybe a 128 bit cipher might offer better performance over the vpn.. but provides a little less security i guess..
Also is the VPN going to push 2Mbps over a 10MBps internet line in which case i 'think' the sg1000 should be able, or do you want to use 100Mbit internet while also using 50Mbit of VPN traffic or bigger numbers in which case it might not..? But again ive got no numbers to back these thoughts up.. Its just the feeling from what i read/remember of comments made around the forum about these devices.