Why don't you try changing up the types of questions that you ask? If you think that you are being too predictable, perhaps it's time for a change in that regard.
Besides, faster isn't always better. Time crunching your candidates may leave out a lot of really great people. Additionally, you may leave out those great candidates who are in demand and who have scheduled other interviews during your limited, two day window.
Keep in mind that just because someone can quickly memorize some fundamentals doesn't mean they can apply them. You want to hire someone who hopefully can take what they've learned and do something innovative and useful with it, and the skills involved in innovation aren't always directly proportional to speed.