Sorry to hear about your results. If you attempted and failed both P4 and P5, I’m not quite sure how one of those can now be your final paper.
It’s not really possible for me to advise on this as it depends on your strengths and preferences. Eg, if you hated F9, then probably don’t go for P4.
P5 had the lowest pass rate in December, but I don’t think that is very important compared to you preferences. As you have now studied both, you should have some ‘feel’ for which you are more comfortable with.