I've seen people pass with your PrepCast scores. That being said, I wanted to score consistently in the high 80's before taking the exam. The actual PMP exam can be the same or MORE challenging than PrepCast depending upon the level of difficulty of the questions you get from the test bank. If you understand fully how to approach the PMP exam questions and you feel that generally you have a good understanding of the processes, high-level inputs and outputs, unique tools, then I would say you are in a "marginal" status to take the exam given those test scores.
I passed on the 1st try with high 80's on my PrepCast full-exams, so I had mastered the following:
1. Exam test-taking time management, PMP answer elimination strategy, trap questions.
2. Could write out the high-level process flow by Knowledge Area.
3. Knew each process MAJOR inputs, outputs and unique tools.
4. Could do CPM problems.
5. Knew the EVM formulas, when/how to apply them, algebra to find missing values.
6. Understood Agile, Predictive philosophies.
7. Understood the various quality management programs (six sigma, JIT, etc.)
8. Had read the PMBOK at least once.
9. Understood controlled and uncontrolled documents, baselines, configuration management.
My general philosophy was to take notes from the PMBOK into an excel spreadsheet (in the form of a question). When I would take a PrepCast exam I would carefully review the test to see why I missed a question (was it in my notes? Did I eliminate two answers but then guessed wrong?). I would then refine or highlight my notes, study, and then take another full-length exam. My scores steadily improved.
Hope this helps you make a decision.