Multiple outlets are reporting that the iPhone 6 will be announced on September 9th. Makes sense to me. The iPhone 5 was announced on September 12, 2012, and the iPhone 5S was announced on September 10th, 2013. My guess would be that they'll announced the iPhone 6 on September 9th and it will be available for purchase on Friday, September 19th.
However, I still don't believe we'll see a 5.5" iPhone 6 on September 9th. We're getting too close to the announcement to have not seen component leaks on the bigger model yet. There have been leaks for several weeks on the 4.7" model. There have also been several leakers and analysts warning of "delays" on the 5.5" model over the past few weeks.
We'll only have to wait 5 weeks to find out. I'm excited.