I have to do both CS and CK, (technically PE for me) for COMLEX and I'll probably end up doing CK for USMLE. The especially fun part about COMLEX-II PE is that it's only offered in Philadelphia, so I also get to pay for travel and lodging.
As far as helping out with the assessment, only in the sense that it helps with the more intangible rhythm part. Of course the two catches with that is my school uses standardized patients (SP) with 6 SP encounters first semester of first year to cover histories (3 patients) and full histories and physicals (second 3), so that advantage shrinks quickly. The second catch is that even a basic physical exam is a lot more than an EMS physical. For example, it isn't just lung sounds. It's lung sounds (at least 4 spots, front and back) and percussion. Similarly, abdominal is 4 quadrants of inspect, listen, percuss, and palpate instead of just look and palpate.
Now once you get into the focus exams, it's worth even less. Orthopedics includes numerous ortho tests (e.g. "drop test" for Deltoid, "empty can test" for Supraspinatus). Neuro includes clinically testing different parts of the brain (rapid alternating movement, memory tests, comprehension test, etc). So the only real benefit is knowing OPQRST before hand, especially since we're given vital signs for the focus exams.
