You don't actually know your sync speeds as they are only in the G.Fast modem. So you must be getting your speeds from speedtests.
Try a wired speedtest on both routers, using an Ethernet cable supplied with the router, here http://www.thinkbroadband.com/speedtest.html . Click on the "Results Page" button at the bottom of the graph you first see and then copy to here just the "Link to this result:" link that you see below the next main graph.
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To phone EE: The local rate landline number +44 207 362 0200 or Freephone +44 800 079 8586 - Option 1 for Mobiles; Option 2 for 4G WiFi; Option 3 for Home Broadband & EE TV.
ISPs: 1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC => 2014: EE 20 Meg WBC