We are sticking with 8Gb sticks as a standard, as the MP3 bibles take up the bulk of the space, and we can get 1x English spoken OT and NT, and 5x New Testaments in Hebrew, Arabic, Turkish, Kurdish and Persian.
Moore’s law is a well known rule of thumb in the IT industry that says data storage devices double in size every 2 years for same cost.
Here’s a useful site that has tracked costs of USB sticks for sale on Amazon US, thats shows this is still true today.
4Gb USB sticks are bordering on obsolete according to February 2013. 8Gb USB sticks are at the sweet spot of about $7 each at the moment which makes the perfect for the amount of content that will be distributed with the xBible project.