Overall, they're pretty much interchangable, with some exceptions. 'schon' can imply an element of surprise. 'Er ist schon da?' - 'Huh, he's already there?'. 'Bereits' is prefered in more formal context, as far as I can tell. 'Wie ich bereits erwähnte' versus 'Wie schon gesagt'. Both of your translations are fine, here, and would mean the same.
Here's a good explanation, too: http://answers.yahoo.com/question/index?qid=20090526204407AAyeeWm