Without doing exactly the same test, I would have to guesstimate the 3 having the same or a bit better life than the 2. I do a lot of reading, but it's typically mixed between Safari and iBooks, with some TweetBot thrown in.
The timed tests I have run on the 3 (doing a variety of the typical tasks) show it can do better than 10 hrs. If you add in any serious gaming, expect noticeably less (which would happen on the 2 also).