Okay, I know you've already bought them, but I'll my 2 cents anyway: You made an excellent choice.
I have both Sibley guides as well (the small one wasn't available when I bought the big one). They aren't perfect, but they are the best I've seen. While photos can be useful, I prefer illustations for a field guide.
Also a note of caution to other readers who are looking for a bird book: I would not recommend the Sibley guides to a beginner/novice birder. They are great if you know what you are looking for before you open the book. If you are experienced enough to narrow your search to a handful of species, Sibley is great for checking the details. If you typically don't have a clue whether that greyish little bird is a flycatcher, a vireo, a warbler, or a sparrow, the one or two species per page format will be slow and frustrating.
I'm still a fan of the Peterson's guide. My most recent one is two or three versions before the current one, but I don't think it has changed much. The "Confusing Fall Warblers" page can be quite useful at this time of year. :-)
BB