As I've explained though, your Ecodrive at 42mm will NOT wear the same as a 41mm Railmaster. I had a Sinn U1 at 44mm but it wore more like a 42mm or less. Another example is the Fortis Cosmonaut B42. It's a 42mm case but the bezel is 44mm so it wears much bigger than a standard 42mm. It really does depend on the watch and the size and shape of your wrist, not necessarily the case size of the watch.
Another point to make is, don't worry too much about original box and papers, these can be sourced from Omega later if you really needed them. I would be more concerned that it has a recent Omega service receipt, and therefore warranty. If it has the original box and papers but no service history, bearing in mind the age of these watches, then the premium paid for the full package is a waste of money. Budget about £300 for a full Omega service with 2-year warranty if it needs one.
I also wouldn't pay more than £2k for a mint, serviced example.
Hope this helps