Thanks Weaver. I remember your setup from some other threads.
The Sharedband setup works in a similar way - my two lines have their own connections, the modems are linked and present a virtual IP to my router behind. I have it set up as a routed connection, you can also present as a NAT address and have the modems act as routers if wanted. The additional firmware on the modems takes care of the aggregation of the links, failover etc, and a server at the ISP takes care of the other end. Single thread downloads go at approx the sum of the two lines, minus some overhead as do uploads. I could add more lines up to a max of approx 20Meg total, but that's dependant on the hardware (TP Link TD-W8968) and it's processing capability, heavier duty routers can support bonding FTTC and faster connections. I don't think Uno support linked PPP sessions, they offer sharedband as their solution for aggregating links.
In terms of stats - the modems are locked down to stop 'fiddling' - I've got a ticket open to gain telnet (& SNMP) access, but it doesn't seem to be working as expected. At the moment all I can get is the stats from the admin page, which don't give a breakdown over time. From my checking, it doesn't seem to be time of day dependant, it's just a percentage of headers have errors, which increments the ES count and annoys DLM.
As far as I am aware nothing round here has changed - but the cable run is long so it could be something further away. Everyone else I know locally seems to also suffer from rubbish connections (if anything worse than mine) and aren't technical so can't offer any insights!
BT/OR are *supposed* to be rolling out FTTH in the next 3 months, so I don't really want to be changing too much as I don't want to get tied into contracts! Worst case I can request to be switched to TT LLU with DLM disabled, which may not fix the HEC errors but will let me stay with a quicker connection, or if it drops much more I'll ditch the aggregated connections and go back to my old Billion router and force it to connect at 6dB!