Hello, 
Thank you so much for your question–and I am extremely sorry for this very late response. Somehow your question did not get answered and I apologize!
To be quite honest, either of these options will be challenging. Organic Chemistry II is a difficult course by itself, and the lab is quite time consuming. I took Orgo II with Bio 171 and it was difficult. I think it might be more doable to pair it with a Biology course (in your case, biochem) because it combines a class that emphasizes problem solving (orgo II) and a more memorization-heavy class (biochem). Pchem is very challenging (arguably more so than Orgo II) because it is similar in that you have to understand the material in depth and apply it on exams. However, it is different in that it is a calculation-heavy class. 
Overall, the choice is yours, and I think it depends on if you want two problem solving courses or a memorization and a problem solving course. Either option will be challenging, and it may be best to consider your own personal strengths. If you have done well in Biology classes in the past, maybe consider taking biochem instead of Pchem. If you are stronger in chemistry, do the opposite. It might also be worth it to take a quick glance at the exam schedule to see if orgo II’s exams are the same or different weeks. 
If you have any more questions, feel free to respond to this post or come to our office hours! Good luck next semester.  
-Cate, PMH Co-President