FWIW, I use a Draytek Vigor 130 modem. By default it's got a firmware that works out of the box for BT, using VLAN 101 and profile 17a and also has the ability to do G.INP / ReTX but it can be configured to use 30a and any SNR tuning as required.
It has a 1gbps Ethernet interface to the router, but I have no idea what the internal connection between modem, CPU and Ethernet is. I do know it's based on Lantiq silicon.
It will present an Web Admin screen and telnet on the interface and give a DHCP address for 192.168.1.0/24 by configuring the actual interface connected to it, while a PPPoE virtual interface on top of that physical interface will still handle the WAN connection. I don't think there's actually a lot of difference between the silicon used in the Vigor 130 and its more expensive brethren, as there's a lot of configuration related to it being a router that's just not possible with 1 port. Hope that helps.
The HG612 (3B that I have) meanwhile only has a 100mbps LAN port...