I agree with podvamp. Go all out for boards. If you don't pass boards, you don't get a residency, end of story. The month of December I studied nonstop! Be OVERPREPARED for boards. In doing so, you will feel so confident for interviews, in my opinion. When boards are finished, take the time prior to interviews to brush up on radiology reads and case studies, as many interviews are presented in this manner from my experience.
As far as visiting programs at this point, it is my opinion that this is a waste of time. Others may disagree. I can't speak for every program, obviously, but for our residency- visitors are typically not ranked very high. This is simply because we just don't have enough time to get to know you. Your stats may be great, but will you fit in? Consider it from our point of view as residents, we will be working with you on a day-to-day basis and we want someone on the team who is not only competent, but who fits our needs on a personal/social level. It would be unfair to judge someone as a whole from a one day visit.
If time allows, however, I think it would be a good idea to re-visit your top programs in the month of Dec. This gives the program a better feeling for how seriously you are considering them. At the same time, most programs are very understanding that the pressure on students this month is unreal, and a visit is not expected.
We've all been there. It's a hell month for sure. But take it one step at a time to attain the outcome that you want. Step 1: boards---- completed. Step 2: brush up for interviews--- Step 3: RELAX, YOU'RE DONE!