Private Network - Mbps Dropped

I recently change the setup to a private network, and added in the remote device (the one not connected to the router/pc with the utility on) with the password. Its connected fine but my Mbps has drop by about 20. It use to be on around the 175-180Mbps mark but now its around the 155Mbps mark.

Why would making it a Private network affect the Mbps. Nothing else has chnaged ie the setup and wiring.