In case anyone should be wondering, my update is that Friday the 14th came and went and I've noticed absolutely no difference. No disconnection at all, no futher email from Orange and normal (for me) download / upload speeds. I've not yet seen any difference to what either the BT Wholesale Line Checker or SamKnows says about my exchange. I'll give it a few more days to see if the information changes.

I didn't leave the computer on all day so I don't know whether the connection was lost (as promised) for up to a half hour period during the day. At least at this stage I've had no need to contact Orange by phone and experience some of the difficulties other people seem to report after they've had to do so following a warning about an exchange upgrade.