iPhone battery life: Siri or iOS 6?
The battery life in iOS 6 has been improved over iOS5 - the big thing will be Siri.

Siri listens to your voice and then sends that information to Apple's servers, which sends it back to your phone. All this costs data and the use of the hardware to accomodate that.

So even thought the battery life has been improved, because you use more features that require more intense processing, you will find that your battery may reduce. In my case I find that I do not use bluetooth as much, so I turn it off when I do not use it.

Hope this helps:-)