It's kinda obvious that the o/s that came with the phone will perform best, no?I love when people on the internet say 'fact' yet they don't add any proof of said 'fact'
I know. That's BS isn't it? If I could, I'd install iOS 7.1.2. on it and call it a day.Well you can't install iOS 7 so that's irrelevant.
Your only options are to stay on iOS 6.0 or update to 8.1.3. For your iPhone 5, you'll probably have better luck battery wise staying on iOS 6.0.
Obviously it depends on your usage, but 7 hours of use is pretty good for an i5 or a 5S. Some people get no more with their iPhone 6 (not the Plus). The Plus has a much bigger battery and is good for 10+ hours.