Five digit numbers always introduce problems because the maximum length of number the human brain can easily handle is 4 digits. For 27 years I worked for an organisation where school premises had a three digit number and I can still remember a lot of these more or less automatically, for example, I might driving through a town and see a road name and automatically think "Ah, centre 379, so-and-so school is down there". But when we switched to five digit ones, no way, even where three of the digits might be unchanged.
