I do get the point, if it ain't broke.
For the uneducated, what is the minimum version of the firmware that is needed to get the 7 digit postcode with version 8 or 9 maps?
Thanks
Maps are independent. You can install the latest maps regardless.
As for Firmware, I think 3800ish was when the full postcode search was added, but it's RNS dependent if it takes that FW or not.
Early A and B RNSs won't take the later Firmwares...the unit either won't take it, or you end up with things not working. Then you get into the problem of having to try and downgrade to get things working again - like Nevigation sound!
My advice would be to physically check which version of the RNS you have before you go any further...then think carefully about updating.