Does anyone know how to wipe the Address book and other user settings from the navigation?

Since I flashed T26.09A onto my system the Arrival time has completely changed - for the worse! It calculates arrival times up to 200% wrong e.g. while driving on a slow road it now calculates the whole route as though it was driven at the slow speed, even when 95% on the journey will be on the motorway.
It seems to just basically look at the distance in miles and calculate based on current speed - pretty useless! This definitely only occured after the V26 beta upgrade and has persisted even after going back to V24 then BMW release V26.

I'm hypothesising that the way the sytem works out the arrival time in some way is linked to the user settings that are not wiped when the flash firmware upgrade is processed. This is similar to the way that the perspective 3D view persisted even when reflashing from the beta 26 to release 26.

I've tried reflashing to V24 then V26. Unplugged fuses 7 and 41, disconnected the battery, but the address book and dodgy arrival time still persist. I guess it must be stored in NVRAM or has a seperate battery backup.

Any ideas? I've just forked out $600 to get Dynamic Routing (BM54) and I can't see how it's going to work properly until this issue is resolved

Ta