Mine's using PPPoA.

Anyway, I think MrSaffron was right -- we've had stability for the last 30 hours (and long periods of stability prior to that) but now the router's syncing at 6Mbits. Previously it was syncing at around 8Mbits.

I'll be honest -- I'm not a speed freak. I was one of the first people in the country to get ADSL at 512Kbit in the early noughties. Back then it was twice as fast as the Internet connection for my entire office. I still think that's pretty miraculous, so 6Mbits feels to me as if I've got my own spur from the Internet backbone.