The software battery meter conditioning should be done when you first get the phone, just to calibrate everything so you don't have to worry about it later on. The Epic has a 1500mha and it all depends on what you do with it. If you don't have a lot of social networking things and other background applications running then you would get better then otherwise.
Here is a review of the battery life of a SGS, should make you happy: Samsung I9000 Galaxy S full battery test ready ? up with the best