PGY-5 residents who failed the Core will also be taking it in June 2014....the numbers I'm seeing for random fails are horrible. Plenty of programs with a all passing, but there are programs with less than half passing. No way this exam is representative.
Also, I would take pass rates VERY seriously as they are a likely indicator of allotted study time. Radiology boards may not be on your radar right now, but you will thank me in 4 years when you pass them.