I've gone back to V26, kept the perspective view and noticed a change. The ETA calculation algorithm seems to work differently. It now calculates the ETA based upon current driving conditions.

For instance before if you had an ETA of say 17:20 at journey start and had a 10 minute delay it would simply update the time to 17:30 as the delay increments. It would not update dynamically based upon the current speed.

Now it seems to update the ETA very regularly based on current driving conditions, I had the ETA fluctuate by up to 30 minutes based on traffic conditions. I think I actually prefer it working this way!

It seems that there are some settings which are kept after a firmware upgrade e.g. Map view selected (perspective), ETA calculations, address book, other user settings, etc. I wonder what else is set 'under the hood' as part of the v26.09T patch that does not have a menu option to unset in V26? I personally would like to enable the TMC Route preference - Dynamic Route, which is part of V26 but no menu option is presented on older versions of the Mark IV VDO systems!