All models of the iPhone 6 Plus except the 16GB base (which, I suspect, is not favoured by those going for the larger screen) are now on 3-4 weeks’ delivery. In contrast, the smaller iPhone 6 seems to be 7-10 days for all configurations. Despite reports that the 5.5-in model has been introduces solely to cater for the Asian market, I think Apple will be surprised at the amount of interest from the USA and Europe in particular. The reason phablets have not been more popular in these markets is that Apple has not had one until now. It will be fascinating to get the sales figures after the weekend.
Postscript: By 11 am on launch day all colours and configurations of the iPhone Plus had sold out at all UK Apple Stores. No details on further availability.