This morning I noticed an extremely low battery usage on my 4S (yesterday night 100% and I took it off the charger, this morning was still 100% after being all night with wifi and 3G on, after a good 15 minutes of use, it dropped to 99% and now is 88% with 1h25 minutes of use (with 3G off).
Yesterday I updated to 6 from 6 beta4 and I can say that this is really great. Let's hope it stays this way!