i was in your shoes for a long time, and last friday finally had the apple store nearby swap out my phone. i wanted to wait a week before posting "official numbers," but after seeing your post, i thought i'd encourage you to consider getting it swapped.
i was seeing 4-5.5 hours of usage on my phone (compared with 6-8 hrs on my iphone 4 under similar usage patterns) and i was getting weird discharge too with it hitting 50% with 3 hours of usage and then really plumetting even after cycling to recalibrate and doing all of the things like resetting the phone and setting up as new, etc.
the new phone, which i haven't even cycled, as already gone through two overnights and after 2 days and 10 hours standby and almost 6 hours of "usage" (on the about /usage page), i still have 20% left. that is a huge improvement.
there is no guarantee that you will experience the same thing, but i think it's worth a shot if you can convince them to swap out your phone. (just back it up, etc.)