There is so much variability in estimating that, it's hard to tell.
-Cell Signal Type & Quality
-Active Widgets
-Rigor of usage (Web browsing, or multimedia device)
-Screen Brightness
-etc...
What is worth noting is that the screen will be using SuperAMOLED, not the more energy efficient PHOLED used in one of the prototypes. Screen size will be increasing by a little bit, and also with a higher resolution.
Also, the SGS4 is being marketed as a "Life Companion", specifically around tracking real time biometrics with a various number of bluetooth accessories. If you're walking around all day with your arm / chest band (requiring bluetooth radio to be On), and exercising with some streaming music service on (requiring one of the data radios on), I'd imagine that extra 300MaH of batter power from the SIII will be easily negated.
But again, experiences may vary according to use.