Ok team... I was holding on to 5.1.1 but our company made 6.1.3 mandatory for all Apple devices, so I had to bite the bullet. I have an iPhone 4S and I must say that with my method for upgrading I'm now enjoying better battery life. I upgraded 10 days ago.
My method is a bit extreme since you'll have to start with your phone as it was brand new and you'll have to start from scratch with your apps, but at least for me it has worked so far.
Quanta's Upgrade Method (tm)
Before starting charge your phone to 100%
1- Start with a Factory Reset (erase all content and settings) with your current iOS version.
2- Delete your current backups and library from iTunes (google delete iTunes library for instructions). The idea is to start with an empty iTunes since you'll setup your phone as a new one.
3- Connect your iPhone to your computer and fire up iTunes. You'll start as if your phone and iTunes are brand new. Let it run the first update check and it will tell you that there's a new version of iOS. Click download and install and let it perform the update.
4- Disconnect your phone and do a new factory reset (erase all content and settings), also delete your backup and library.
5- Do the basic setup on the phone again and reconnect to the computer and set it up in iTunes again.
6- At this point I started installing my apps via Wifi. I've installed the basic apps that I use on a daily basis: Whatsapp, Viber, Skype, Dropbox, Google Maps and YouTube. And just a couple of games, Cut the rope, fruit ninja and Angry Birds.
7- I've also set my two main Email accounts. The one from work (Exchange) and my personal Gmail account (on Exchange mode). Both have Push Email active. My Gmail accounts is also synching my contacts.
8- I've activated iCloud for Find my iPhone and also to sync my notes and bookmarks. All other options from iCloud are off.
9- Last step was to charge again to 100% and then use it normally until the phone shuts down, this will allow you to calibrate the battery circuit under the new OS
With this method I'm getting through the day easily with my phone. I have 3G and data ON all the time, and I receive quite a few emails daily. I must say that with the new OS I saw on my standby usage stats the words "1 day and x hours..." For the first time, since with 5.1.1 I would only get a max of 18-19 hours of standby, even with light use.
This weekend I'm planning to apply the same method to upgrade my iPad 3 to 6.1.3 (it's also on 5.1.1), Ill report the results. If you have any questions let me know.