when you say "how concerned should you be?" it depends what you are speaking in reference to.
if you are worried about your study score, I wouldnt worry too much about your sac score, worry about your sac ranking. hard sacs scale up. in fact at the end of the day, your raw sac marks dont matter. all that matters is your ranking in your cohort for the subject.
someone who is ranked first in their school in methods but has a sac average of 70% is in the same position as someone ranked first at another school with a sac average of 100%, it will be the exam that separates them.
if you are worried about your level of preparation for the exam, harder questions in sacs means that the exam will be relatively easier.
so overall you are probably in a better position if your school has hard sacs with an average mark of 60%