Hi Lori,
Great write up and to the point.
Think we can safely say that performance layer 4, forwarding IP, forwarding layer 2 virtual servers when configured, the BIG-IP device is not used as a full proxy (i.e. any traffic which transmits at layer 4 and below is transmitted via a packet by packet proxy mode). To further add, FastL4 profile when configured on a VS simply forwards a packet from ingress to egress. (i.e. does not inspect tcp connections and create new connections to the backend servers; simply forwards traffic out)