I would like to point out that caching one bitmap per page will be the preferred solution for a different but important reason: You don't want to have your laptop GPU running at 100% while viewing static text. Fidelity is nice, but I don't think you'll convince many people with an ebook reader that drains your mobile device's battery like that.
I don’t believe this is a problem. It will only need to render it when things change—so maybe the GPU will be sitting at 100% while you’re flipping through pages, but other than that typically very brief time, it should be at 0%.
