I've never pre-ordered anything from BB/FS before so I don't know how much pre-order stock to expect. I'm sure games like Destiny will have a ton. And I'm lucky since I only really want WWE 2K15 and that seems like a niche thing.
Hm, well, the $10/15% off pre-orders from earlier in the year were limited. Mario Golf went fast, for example. I'm not sure about these E3 deals... FS and BB probably have a number in mind from each publisher in terms of stock, and likely will divide that number up as far as online stock goes, eg. say they're getting 50,000 copies of The Witcher 3; 25,000 PS4, 20,000 XB1, 5,000 PC; they would allocate about 70-80% of that to us on the first day of the deal, then the rest through out the week of the deal. I think. But it wouldn't be the same for every title, you know; they'd order much more Call of Duty: Advanced Warfare than Monster Hunter 4, for example.
It would be wise to choose titles, that you want in the first place, from smaller publishers, ie. Atlus, Bandai Namco, even Nintendo. The Desiny's and Call of Duty's won't run out.