"what is the best page file size for my PC?"
The final word on understanding the paging file and it's size belong to this well know Microsoft fellow and expert Mark Russinovich.
Read his explanation of the paging file by clicking the link and after he has explained it's use and how it works, he finally has something to say on some of the common advice given on setting it's size:
How Big Should I Make the Paging File?
"Perhaps one of the most commonly asked questions related to virtual memory is, how big should I make the paging file? There’s no end of ridiculous advice out on the web and in the newsstand magazines that cover Windows, and even Microsoft has published misleading recommendations. Almost all the suggestions are based on multiplying RAM size by some factor, with common values being 1.2, 1.5 and 2. Now that you understand the role that the paging file plays in defining a system’s commit limit and how processes contribute to the commit charge, you’re well positioned to see how useless such formulas truly are".