I have this exact problem, and the exact maximum speed you get (95mbit) doing tests at 5am and other uncommon times and anywhere from 5mbit-40mbit during peak times. Even right now at 10:55pm getting 13mbit speed test
modem syncs at 109/40, getting a lot of FEC errors in the DSL section of the router, could be normal? this vectoring business? not related to conjestion but wondering if you have the same (assuming you're FTTN connected)
Roughly where do you live? I'm having this issue in Belmont NSW. (Hamilton NBN POI)