Well, that was a day.
We only gone and done it again - for the third time in three years we have payed up and officially reserved a house. The difference this time is that our progress is not contingent on the sale of another property - and so, we are in control of our own destiny.
As with all choices, there are compromises that are necessary - but they are not huge, and it does mean that we get a house built to very exacting standards. Now all we have to do is wait for it to be built - which will, no doubt, seem interminable.