Yep, everything will move over fine, it doesn't care what carrier it's on. You could even restore that backup to an iPod Touch or iPad if you wanted. The only requirement is the new device has to be running the same or a newer iOS version then the backup came from.

And yep, by using the iTunes encrypted backup, all data comes over including passwords.

I'm going to be curious about your upgrade impressions with the 4 year leap you are making. I have a hard time remembering back to the 4s being new, that was 3 states and 5 addresses ago.

If you do want to hold off till next Friday on making the decision, I'll have my 6s then. Could do coverage testing. I'm really curious to see how band 12 helps. It just lit up here in Seattle about a month or two ago, and the 6s is the first iPhone to support it.