The decision is up to you entirely. In making your decision, consider this question: If you gamble and rates go up to 6.5% would you still be able to afford the home? If not then lock in right away. If you can afford to take the gamble then ask yourself this question too: Which would upset you more - if you locked in today and rates went to 5.5% this week or if you didnt lock in and they went to 6.5%? Make your decision based on that.
Just my opinion: It's a lot easier to go back and renegotiate or even refinance later if rates come down, but if they go up what's gone is gone