Re the speeds on FTTC dropping to ADSL levels, you've either come across someone with a line problem or a long line. The "impacted" figure for your line is what Openreach think might happen once there are a fair number of FTTC users on your cabinet. So in the normal run of things you've no need to worry about that aspect.
The difference in performance between Be and BT should not have been that great. Maybe it is worth posting about it in the General Chatter (for the widest audience) or the BT forums about that as a separate issue. I can think of a few possible reasons. It could be that whatever is causing it would have a bigger effect on FTTC, or none.
On FTTC your connection speed is determined largely by your distance from the Fibre cabinet. All the equipment in the cabinet and the fibre as far as the exchange is Openreach, even for the LLU suppliers. At the exchange it is handed over to the (wholesale) supplier using a "GEA link". From there it goes into the BT Wholesale WBC system or the LLU supplier's backhaul.
Currently as far as I know that means BT Wholesale, Sky, TalkTalk and Zen, though I think in many exchanges Zen still use BT Wholesale.
There are also Daisy and Coms wholesalers, used by some of the smaller ISPs. Those two don't have their own handover points in the exchange, but AIUI take a feed from BT Wholesale or TalkTalk at the exchange into their own backhaul.
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UnLim Fibre (FTTC). Sync ~ 59.4/14.4Mbps @ 600m. - BQM
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Edited by RobertoS (Mon 30-Dec-13 00:04:48)