I re-read my first posting in this thread, and I realised that things have changed a bit since then, back in 2012. I now have a third line IP-bonded into the group. The Firebrick router ties the three incoming pipes together, handles IPv6 and IPv4 routing and firewalling, and deals with upstream load-sharing across the three lines. I have an adequate sized block of IPv4 addresses (no NAT) and a /48 for IPv6.
As for modems, I now have three DLink DSL-320B devices which are currently ds-syncing ~2100 ds, anyway in the BTW IP profile 1750 band, occasionally touching 2272 but this is only sustained for a week or so, sometimes more, sometimes less. Combined ds ip throughput comes out at something around 5.2 Mbps according to the speed tester
http://speedof.me, other speed testers are lower. US throughput varies between lines, and combined US IP throughput varies wildly according to which speed tester is chosen, but is in excess of 700 kbps.
I’m still stuck with BTW 20CN ADSL1, no choices, no LLU on offer at this exchange. I take the BTW IPStream Max Premium option on all three lines, which gives me traffic priority on the A&A network as well as BTW’s. I also have BT Enhanced Care on one line as a just-in-case.
I also now have an A&A 3G SIM (on the Three network) which routes a single static IPv4 from an iPad straight through to the A&A network, again no NAT or mobile network private addressing in the way. This just works very cleanly and reliably, no fuss and has the same continuous quality monitoring as A&A’s DSL lines.