Our school required a 2-month preceptorship and an optional research project. I'd take it a little easier (no need to study hardcore), but I found it's one of the best times in med school to start getting involved in research. If you're thinking about a competitive residency, research will most likely be recommended.
I touched on this in another thread, and I'm sure its been discussed to death in some buried thread that I didn't bother to look up, but: does graduate research help, in terms of residency placement? Is clinical research really the "gold standard"?
(My MS required a published thesis, but it was in a field of Biochemistry... no trials.)