The ProxySG has RFC-1323 enabled, but it's only requesting a scaling-factor of 1 when connecting to webservers, resulting in slow download speeds for large files on the network.

Window-Scaling behaviour in SGOS with RFC-1323 enabled is currently as follows:

Inbound Connections
The ProxySG will accept whichever scaling-factor is requested by the client.

Outbound Connections:

With ADN enabled - the ProxySG will request a window scale of 6 by default.

With ADN disabled - the ProxySG will request a scaling-factor of 1 by default.

To allow for the use of larger scaling-factors, the TCP window-size should be increased. For example:
#(config)tcp-ip window-size 4194240

(TCP window-size is 65535 by default)